Downing Street has defended its failure to inform Italy ahead of a hostage rescue operation in Nigeria which ended with the deaths of Briton Chris McManus and Italian co-worker Franco Lamolinara.
Italian President Giorgio Napolitano said today that the UK's failure to tell Rome was "inexplicable" and demanded a political and diplomatic explanation.
As the diplomatic row between Italy and Britain deepens, Italy's foreign minister Giulio Terzi has waded into the ruckus, demanding "the utmost clarity" from Britain as to why Italian authorities were not told of the rescue mission, reports the BBC.
The foreign minister's insistence for information to be sent "as soon as possible, in the coming hours" follows talks with British foreign secretary William Hague.
The UK's ambassador in Rome is understood to be in contact with Italian authorities, but Downing Street said it had so far received no official complaint from the government of Prime Minister Mario Monti.
The two construction workers died yesterday as Nigerian troops and UK Special Boat Service (SBS) commandos launched a rescue mission to end their nine months in captivity in the West African country.
Prime Minister David Cameron's official spokesman told reporters today that Britain and Italy had been in contact ever since the men were first kidnapped last May, and that the Government's Cobra emergency committee had met around 20 times to discuss the case.
"We contacted the Italians yesterday as the operation was getting under way, but this was a very fast-moving situation," said the spokesman.
"Our priority was to respond to the situation on the ground and to do everything we could to try and secure the safe release of the hostages."
Mr Cameron said last night that Mr McManus and Mr Lamolinara had been in "imminent and growing danger" and an opportunity had arisen to attempt to rescue them.
"The terrorists holding the two hostages made very clear threats to take their lives, including in a video that was posted on the internet.
"Preparations were made to mount an operation to attempt to rescue Chris and Franco. Together with the Nigerian government, I authorised it to go ahead, with UK support."
Exact details of how Mr McManus died remain unclear, but Mr Cameron said initial indications were that the contractor and Mr Lamolinara were "murdered by their captors, before they could be rescued".
Members of the SBS are understood to have been involved in the operation, which unfolded in the city of Sokoto, in the north-west of Nigeria, along with Royal Marine Commandos and members of the Nigerian military.
It is thought the bid to rescue the men may have been brought forward because the kidnappers - believed to be members of a jihadi group associated with al Qaida - became aware that the net was closing around them, though this was not being officially confirmed in London today.
There were reports of a house being surrounded by military and the sounds of gunfire heard before an ambulance was called, according to the Associated Press.
Downing Street said today that there were government-to-government contacts between London and Rome as the operation got under way, and that Mr Cameron later spoke to Mr Monti by phone after it was learned that the hostages were dead.
Mr Cameron's spokesman said he was not aware of any request from Rome to halt the operation or of any complaint from Mr Monti during yesterday's phone call.
Mr Cameron did not offer any apology for the way in which the mission unfolded.
It had been clear for some time that one option was an attempt to rescue the two men, and Downing Street was not aware of Italy raising any objection to a possible mission, said the spokesman.
Mr Monti disclosed the lack of prior warning in a statement last night in which he said UK and Nigerian authorities had determined the operation was the "last window of opportunity to save the hostages' lives".
And Mr Napolitano told reporters today: "The behaviour of the British Government in not informing Italy is inexplicable.
"A political and diplomatic clarification is necessary."
Mr Cameron's spokesman told reporters at a regular Westminster briefing: "We had been in contact with the Italians on a regular basis over the past nine months. We have had many, many meetings in the UK on this issue. There have been around 20 meetings of Cobra to discuss this particular case and throughout that period we have been in contact with the Italians.
"An option was always a rescue operation. We have been keeping them informed throughout."
He added: "Things moved quite quickly in recent days and we had to respond to that... The Prime Minister was asked for authorisation and gave that authorisation, but this was a Nigerian-led operation.
"In any situation such as this, we need to take the advice of those people on the ground closest to the situation. Their very strong advice was that it was important to act and to act quickly and that that was the best chance of getting these people out.
"Early indications are that both men were murdered by their captors before they could be rescued."
Mr Cameron offered his "sincerest condolences" to relatives of the hostages, saying they had "endured a terrible ordeal", after details of the failed mission emerged.
In a statement, Mr McManus's family said they were "devastated by the news of Chris's death" but confident that "everything that could be done was being done" during their 10-month ordeal.
The family, who live in Oldham, added: "We are also aware of the many people who were working to try and have Chris returned to our family and his girlfriend. We would like to thank all of them for their efforts."
Asked how the Prime Minister felt personally about what had happened, Mr Cameron's spokesman said: "Clearly these are very difficult decisions. He has taken a close interest in this case over the course of the last nine months.
"Ultimately we had to make a judgment and he had to give the authorisation based on advice from those people on the ground."
Five members of a group known as Boko Haram are understood to have been arrested by Nigerian security forces, and the Reuters news agency said some suspects in the kidnapping were held a few days before the rescue attempt. Some of the hostage-takers were killed in the operation.
Nigerian President Goodluck Jonathan condemned the killing of the hostages, adding: "The perpetrators of the murderous act, who have all been arrested, (will) be made to face the full wrath of the law."
Mr Cameron's spokesman said: "Who is responsible for what happened? We need to take a step back and say that the terrorists themselves are responsible for this.
"We should be in no doubt that it is those people who are responsible for what happened."
Any investigation into the handling of the operation would be a matter for the Nigerian authorities, he added.
Mr McManus, a contract worker for the construction company B Stabilini, was kidnapped by a "horde of gunmen" in May last year.
Raiders stormed his apartment in Birnin-Kebbi, in the north-west of the country, and captured him along with Mr Lamolinara.
A German colleague escaped by scaling a wall but a Nigerian engineer was shot and wounded in the raid. The men were building a bank in the city.
In December, a Nigerian group calling itself "al Qaida in the land beyond the Sahil" announced that it had captured Mr McManus.
It released a hostage video to the Nouakchott News Agency claiming it had kidnapped the Briton and showed a blindfolded and bearded man in an orange vest.
Three men in dark clothing stood behind him, armed with rifles and a machete.
It was reported that the man pictured in the video called for the UK Government to respond to the demands of the group, so they would spare his life.
He also asked for the British people to pressure the Government to answer the demands of the group so he could return to his family.
Boko Haram, the group which Nigerian President Goodluck Jonathan claimed kidnapped the Britain and Italian is currently not on the British Government's list of international terrorist organisations banned under the Terrorism Act 2000.
A Home Office spokesman said: "We constantly keep the list under review."
However Boko Harem has now denied they were involved in the attacks.
"We have never taken anyone hostage. We always claim responsibility for our acts," said Abul Qaqa, spokesperson for the militant Islamist group.
According to Sky News Qaqa told reporters in a conference call:"We know how to settle our scores with anybody. Therefore the allegation that the kidnappers were members of our group is ridiculous."
Defence Secretary Philip Hammond said the Italian authorities were "notified about what was going on".
He told Sky News: "They did know that the operation was under way and judgments had to be made.
"Sadly the outcome, of course, was not the one that we were hoping for but nobody has ever pretended that rescuing hostages from armed kidnappers is a risk-free business."
He added: "We will obviously want to analyse ourselves exactly what happened, to learn any lessons that can be learned for future similar-type situations.
"We will communicate everything we can to the Italians so they have a full understanding and a full picture of the pattern of events over the period from when the first intelligence emerged, through its confirmation and the operation on the ground starting."
Defence Secretary Philip Hammond disputed the Italian president's comments that Britain's failure to tell Italy of the rescue bid was "inexplicable".
He told the BBC: "Well it isn't inexplicable. It's completely explicable what happened.
"It's very unfortunate, but it's completely explicable."
Asked why the Italian authorities were not consulted, he said: "The Italian government was kept informed throughout the operation as the intelligence emerged and then as the decision was taken to act, the Italian authorities were informed."
However, Mr Hammond said that although they were told about the operation, they did not authorise it.
"They were informed on it," he said.
"I don't think they specifically approved it, they were informed of what was happening."
The Defence Secretary told the news channel why the decision was made so quickly: "There was intelligence that they were about to be moved, possibly executed and therefore the decision was to go in, aware of course that there were huge risks.
"Hostage rescue exercises always have huge risks attached to it but the decision was made that the best chance of saving their lives was to act."
He added: "A window of opportunity arose, but very sadly and unfortunately, it didn't turn out as we hoped, but everybody involved gave it their very best effort to try and get them out alive."
Speaking in Gateshead as he arrived for the Liberal Democrat spring conference, Deputy Prime Minister Nick Clegg told Sky News: "Everyone's heart goes out to Chris McManus and his Italian colleague who lost their lives in these very difficult and tragic circumstances.
"We tried to do everything as a Government to first find out where they were and then to move quickly to seek to rescue them, because of course they had been held under brutal conditions for a very long period of time.
"But on this occasion, as the Prime Minister explained, unfortunately it appears the hostage-takers took the lives of these two men before the rescue."