Senior Labour figures have privately pledged support for airstrikes in Syria with half of Jeremy Corbyn's shadow cabinet ready to back intervention, according to reports.
Tory ministers have been told they will win support for action to tackle Islamic State, also known as Isis, if a coherent plan is drawn up, the Sunday Times said.
It names shadow foreign secretary Hilary Benn and three of his team - David Hanson, Pat McFadden and Diana Johnson - as among the figures expected to back such a move.
"There is a majority in the Commons for airstrikes in Syria if Cameron has a proper plan for targeting Isis," a shadow cabinet member told the Sunday Times.
"You would get half the shadow cabinet supporting it."
Foreign Secretary Philip Hammond said the possibility of a fresh vote on British military action in Syria is kept under constant review following talks in London with US Secretary of State John Kerry.
Backing intervention would put Labour MPs at odds with their new leader, who has just ended a stint as chairman of the Stop the War Coalition.
Mr Corbyn was due to speak at the organisation's annual general meeting in central London but pulled out to prepare for Labour's party conference.
He will use his first appearance as leader at the autumn gathering in Brighton to set out more details of his plans for rail renationalisation.
In a bid to create a "people's railway", franchises would return to public ownership as they expired if Labour takes power, he will say.
Mr Corbyn told the Sunday Mirror: "We know there is overwhelming support from the British people for a people's railway, better and more efficient services, proper integration and fairer fares.
"On this issue, it won't work to have a nearly but not quite position. Labour will commit to a clear plan for a fully integrated railway in public ownership."
Mr Corbyn has endured a turbulent first week at the helm of the party with the row over his failure to sing the national anthem at a Battle of Britain commemoration dominating headlines.
Polling found that half of Britain believes the republican should have joined in with the song during the service at St Paul's Cathedral.
The left-winger's election as Labour leader has seen support for the party go up by one point but the Conservatives are still 12 points ahead on 42%, the research also found.
In the study for the Sunday Mirror and Independent on Sunday, ComRes found that 50% of voters believe he should have sung the anthem while 29% disagreed.
But 52% said Mr Corbyn was making people more interested in politics, compared to 22% who disagreed, and 41% agreed that he offered a "positive difference from other politicians" with 31% disagreeing.
Among those most likely to vote, 42% believe the Labour leader is a danger to national and economic security - the attack lines used by the Conservatives in the wake of Mr Corbyn's victory.
The poll also found that around twice as many Britons say they are unfavourable towards Mr Corbyn as say they are favourable at 42% to 24%.
His net favourability is minus 18 compared to minus seven for Prime Minister David Cameron.
Tom Mludzinski, director of political polling at ComRes, said: "His Marmite effect continues in leadership as it did during the campaign.
"This poll reveals that the Conservative attacks on the danger the new Labour leader poses are having some impact, he is also offering a breath of fresh air to politics for many people."