Jeremy Corbyn has risked a fresh internal row by suggesting Labour should consider pulling its support for the ongoing British military action against Isis in Iraq.
Questioned by ITV for a pool video clip on Tuesday, the Labour leader said Parliament should "look again" at the RAF airstrikes.
As the Government appeared to be on the back foot over its own decision to postpone a Commons vote on Syria, Mr Corbyn drew raised eyebrows on his own side by hinting that the party could dump its agreed line on Iraq.
"What's being done in Iraq is done by the Iraqi government and currently supported by the British government," he said.
But in a refererence to the fact that he was among 24 Labour MPs who refused to authorise the military return to Iraq under Ed Miliband in 2014, he added: "I did not support it when it came up."
Asked if the UK's current military action in Iraq should stop, Corbyn replied: "Well, I'm not sure how successful it's been because most of the action now appears to be moving into Syria, so I think we have to look again at that."
His remark could trigger further dissent from shadow cabinet ministers who strongly support the UK's involvement in the anti-ISIS coalition in Iraq and who are already uneasy about Mr Corbyn's move to ditch Trident.
A spokesman for the Shadow Foreign Secretary, Hilary Benn, made clear that he believes the RAF bombing campaign against Isis in Iraq should continue.
When asked by the The Huffington Post UK about the Labour leader's comments, Benn's spokesman said: "Of course, Hilary believes the government should always be reviewing these things."
But he added: "His judgement remains the same as it did when parliament overwhelmingly voted, and Labour MPs overwhelmingly voted, to agree to the request for assistance from the Iraqi government to resist the invasion by ISIL."
In September 2014, MPs voted 524 to 43 – a majority of 481 - to launch military strikes in Iraq against the Islamist extremist group. Of the 43 MPs who opposed the action, 24 were Labour - including Mr Corbyn.
Number 10 today pounced on Mr Corbyn's comments. The Prime Minister's official spokeswoman suggested any move to abandon the fight against ISIL in Iraq would endager the UK's national security at home.
"The Prime Minister has been clear that he’s focused on national security and is focused on what the government can do to protect the British people from the threat of ISIL. Action against ISIL in Iraq is part of that and it was backed by a majority of 481 MPs," she said.
"We are taking action against ISIL in Iraq for a number of reasons. We have always been clear that ISIL pose a threat to the UK too.”
Mr Corbyn's comments came after Downing Street earlier moved to deny claims David Cameron had abandoned plans to hold a Commons vote on widening the RAF campaign from Iraq into Syria.
But George Osborne confirmed that the Government had no current plans to bring the Syria issue back before MPs. "At the moment it is not clear that there is a majority for it," he said.
Today the Commons foreign affairs committee also cautioned that the prime minister should not ask MPs to back military action against Isis in Syria until he can show there is a clear plan both to defeat the jihadists and to end the bloody civil war.
Crispin Blunt, the committee's Conservative chairman said: "We need and owe it to our servicemen not to ask them to put their lives at risk if there isn't the prospect of their service being used effectively."
Earlier today, Labour clashed with the BBC over claims that it has given the Stop War Coalition a veto over the party's policy on UK military action in Syria.
The broadcaster reported that shadow foreign minister Catherine West told a meeting last night that Labour would "consult" the peace campaigners before making any decision on extending RAF strikes from Iraq.
But Labour sources have told The Huffington Post UK that Ms West is upset with the way the BBC reported her words, and she claims that she was referring to consulting Syrians rather than Stop The War.
At the event in Parliament, Ms West had said Russia's intervention in Syria meant that Cameron's plans to stage a Commons vote on UK action now seemed a "remote" prospect.
She added: "Obviously, if that proposal does come forward, then we will need to speak to you and talk to you about what your view on that is."
Labour says that the "you" in her remarks was the Syrians in the room, many of whom have argued for more British help.
A Labour source said: "Catherine is clear that she was talking to the Syrians in the room who were being shouted down by some of the people present who seemed unwilling to listen to the voices of those most affected by the civil war."
"Hilary [Benn] visited refugees in the Zaatari camp and in the host community in Jordan last week where he met some of the people who have been so traumatised by this war. He is clear that David Cameron has not given the Syrian crisis sufficient attention and has failed to come up with a comprehensive plan."
Activist Peter Tatchell also tweeted from the meeting that Syrians were being silenced by Stop the War campaigners during the event.
He told The Huffington Post UK today shadow international development secretary Diane Abbott would not allow Syrians to speak. "I was shocked, surprised and saddened by Diane Abbott's unwillingness to invite Assad's victims to express their opinions.," he said.
"Not listening to victims of Assad’s war crimes is arrogant, insensitive and appalling. It has a whiff of 'we know best' and Syrian views 'don’t count'."
Labour also "smell a rat" over the overnight stories that Mr Cameron has shelved plans for a Commons vote on fresh military action in Syria.
One source said: "It is all part of the desperate political management exercise the Government have engaged in for three years now, where the question has miraculously been 'what will Labour do on airstrikes', when they cannot answer 'what is your actual plan to win the peace?'”