Diane Abbott, the shadow international development secretary, has been told by a fellow Labour MP to stop behaving like an “internet troll” after she accused some of her fellow MPs of wanting to side with David Cameron and bomb Syria.

Abbott, one of Labour leader Jeremy Corbyn’s most vocal supporters in the shadow cabinet, responded to an article co-authored by Jo Cox, a new Labour MP, that called for the government to consider safe havens in Syria to protect Syrians from air attacks by President Assad.

The article, which was published in the Observer and co-written by former minister for international development Andrew Mitchell, appealed for protection of civilians to lie at “the centre of the mission”. It continued: “Some may think that a military component has no place in an ethical response to Syria. We completely disagree”.

Abbott tweeted it was sad that “Labour MPs want to support Cameron in his long held desire to bomb Syria”.

John Woodcock, the Labour MP and chairman of New Labour pressure group Progress, hit back, saying: “Plight of refugees more important than Westminster bubble. You’re shadow int development sec not an internet troll.”

Woodcock’s response underlines the continuing tensions within Labour in the wake of Corbyn’s election. A small number of his supporters on social media were calling for MPs who backed military action to face reselection.

The joint article by Cox and Mitchell aimed to spark a strategic debate about Syria rather than focus specifically on whether the UK should join its coalition partners, notably the US and France, by extending its bombing campaign against Isis In Iraq to Syria.

In a House of Commons debate on Syria on Monday, Cox is expected to say Labour should not allow the experience of Iraq to blind it to the need to back the use of military force for humanitarian ends, as it did in Bosnia, Kosovo and Sierra Leone.

She will argue that, for too long, Cameron has put the issue on the “too difficult” pile following his failed attempt to intervene militarily in 2013.

The prime minister is undecided on whether to ask the Commons to vote to back UK involvement in airstrikes against Isis in Syria and in defence of the democratic regime in Iraq.

Any Commons vote would be unpredictable, but Labour has said it will only support such strikes if there is an explicit mandate from the UN security council, and clear strategic objectives.

Cameron remains convinced, along with the Americans, that Assad must step down as part of the transition to a new government, but some Conservative MPs and military planners argue that the recently strengthened Russian protection of Assad makes this an unrealistic objective and the immediate goal must be the destruction of Isis and other terrorist groups in northern Syria, even if this means temporarily abandoning any attempt to get rid of Assad.

Iran believes the US-led bombing coalition is not serious about destroying Isis unless it is sure Assad will go as well, and so has been holding off.

Cameron has the option of seeking a vote in the Commons, but will need to know if Corbyn will treat the issue as a conscience vote, and if not, how many Labour MPs are willing to rebel. The chief whip, Rosie Winterton, is sceptical that such an issue could be conducted on the basis of conscience.

The government has been holding unofficial discussions with potential Labour supporters of UK military action both to test the numbers and its precondition for support.