British forces are unable to mount a rescue attempt to free the hostages held by Islamic State (IS) militants because they do not know where they are being detained, Foreign Secretary Philip Hammond has said. Following talks with international foreign ministers in Paris, Mr Hammond said the Government would have been ready to consider "all sorts of options" if they knew where the hostages were.
IS extremists - who have killed British aid worker David Haines and two American journalists - are now threatening to kill a second UK hostage, former cab driver Alan Henning, who was snatched while travelling with an aid convoy in Syria. Mr Hammond told reporters: "We don't know where he is. Obviously, if we knew where he was, we would be able to look at all sorts of options but we don't know where he is.
"We have considered every possible option to support these kidnap victims - both British and others - and if we knew where they were, it would be a different story but we don't know where they are."
Mr Hammond said Mr Henning's family was "going through hell" but that they understood there was a limit to what the Government could do to help him. "It is a terrible time for them. We are doing everything that we can to protect him," he said. "They understand, because we have explained to them in detail, the limitations of our abilities. We are dealing with a very barbaric organisation whose values are completely different from ours."
Foreign ministers from more than 30 countries attended the talks in Paris intended to build support for international action against IS - also referred to as Isis of Isil (the Islamic State of Iraq and the Levant) - which has taken large swathes of territory in Syria and Iraq.
Mr Hammond said he had made clear that Britain would play a "leading role" in the gathering coalition, although he would not be drawn on whether the Government was ready to join US air strikes on IS in Syria. "I have said already in Parliament that would be an order of magnitude more difficult than air strikes in Iraq for all sorts of reasons - military, legal and technical - but we haven't ruled it out," he said.
"We haven't made a decision yet about how we will best contribute to the coalition effort against Isil. But I have said this morning in the meeting that Britain is clear that it will play a leading role in this coalition."
Addressing an audience at a private event at Harvard University, the Home Secretary Theresa May said: "On Saturday night, I heard the terrible news that Isil had carried out another murder of a hostage, and shortly afterwards it was confirmed that the victim was David Haines, a British humanitarian worker.
"This was an absolutely barbaric act, and everyone's thoughts are with David's family. And of course, David's death followed the murders of the American citizens, James Foley and Steven Sotloff. Our message has to be clear. The United Kingdom, like the United States, will not allow these grotesque acts to stop us from keeping our homelands secure and stopping the march of this brutal ideology."
Opening the talks in Paris, French president Francois Hollande said the need for action to tackle IS was urgent. "The terrorist threat is global and the response must be global. There is no time to lose," he said.
Iraqi president Fouad Massoum called for the continuation of air strikes against IS militants in the north of his country. "We are asking for airborne operations to be continued regularly against terrorist sites. We must not allow them to set up sanctuaries. We must pursue them wherever they are," he said.
"We must cut off their financing. We must bring them to justice and we must stop the fighters in neighbouring countries from joining them."
US secretary of state John Kerry has been urging allies - especially Middle East and Gulf states - to show a united front and an American official said several Arab countries had offered to join air strikes. However Iran's Supreme Leader Ayatollah Ali Khamenei disclosed that he had received a request from the US to join the fight against IS but said he had rejected it because of Washington's "unclean intentions".
Nevertheless Mr Hammond said that he hoped Tehran - a key player in the region - would still be "co-operative" with the coalition's objectives. "It was always unlikely that Iran would become a fully-fledged member of the coalition," he said. "But I think we should continue to hope that Iran will align itself broadly with the direction the coalition is going and that we can expect Iran to be co-operative with the plans that the coalition is putting in place, if not actively a part of the coalition."
Downing Street said that heart of the international strategy was building support for forces in the region who are currently engaged in fighting IS. "The people who must rightly be in the lead in terms of boots on the ground are Iraqi boots on the ground and Kurdish boots on the ground, and we need to put together the approach that best supports that," the Prime Minister's official spokesman said.
Mr Haines' teenage daughter Bethany left a message on a Facebook page dedicated to her father, saying she had been "touched" by the support she has received. She wrote: "Hi, I'm David's daughter who lives in Perth I was really touched by the messages of support during this hard time I know my dad would be really touched and grateful."