Shadow foreign secretary Hilary Benn has insisted he will not resign in protest at Jeremy Corbyn's opposition to bombing in Syria.
Mr Benn backs military action against Islamic State and suggested that Labour may end up agreeing to a free vote on the issue despite the party's leader's hopes for a "common view".
David Cameron has urged wavering Labour MPs to back military intervention in Syria, telling them to "vote on the basis of the arguments".
The Prime Minister said there was a "compelling" case for airstrikes and insisted MPs would allow the country to do the "right thing" if they supported them.
Speaking in Malta, where he is attending a Commonwealth summit, Mr Cameron said: "I believe there is a compelling case to take the effective action to keep our country safe."
Mr Corbyn is struggling to contain a shadow cabinet revolt after saying he could not support RAF action against IS.
The shadow cabinet will meet again on Monday, but it appeared that Mr Corbyn would face a rebellion from his top team if he tried to force them to oppose action.
Mr Benn told BBC Radio 4's Today programme: "I'm not going to resign because I am doing my job as shadow foreign secretary."
He added: "This is very complex, it is very difficult and each individual in the end will reach their own decision about what they think the right thing to do is.
"I respect those who take a different view, I genuinely do."
If Mr Benn refused to resign and then voted for military action against a whip imposed by Mr Corbyn, the leader would have little choice but to sack him.
Asked whether Mr Corbyn would be forced to allow a free vote on the issue, Mr Benn said: "That remains to be seen because the shadow cabinet will continue its discussions on Monday and it may be that that is where we end up."