Jeremy Corbyn has signalled for the first time that Labour could support forms of military action in Syria without UN support if Russia blocks a security council resolution.

Taking a more flexible approach to UK military involvement in the Syrian civil war, the new statement urges David Cameron to try again to win support for a new UN resolution allowing military action, and affirms that the party supports the creation of safe zones within Syria to protect Syrians who have had to flee their homes.

In an article in the Guardian on Monday, Diane Abbott, the shadow international development secretary, rejected the idea of safe havens when proposed by Jo Cox, one of the backbenchers trying to assemble a broader Labour policy on Syria that does not just wait to react to government proposals.

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The new positions, an attempt to assert a collective shadow cabinet policy, are laid out in a new article on Comment is Free by the shadow foreign secretary, Hilary Benn, and follow a meeting on Tuesday morning between Benn, Corbyn, the shadow lord chancellor, Lord Falconer, the shadow attorney general, Catherine McKinnell, the shadow defence secretary, Maria Eagle, and the shadow chief whip, Rosie Winterton.

In a bid to underline this as the agreed Labour leadership position, Corbyn issued a brief statement, saying: “I met with shadow cabinet colleagues today and Hilary Benn is setting out the position today.”

The new stance, taking into account the unexpected Russian air campaign in Syria in defence of Assad, is also significant since it is the Labour policy with which the prime minister will have to work if he is to build a clear consensus in the Commons for further UK military action as part of a wider diplomatic plan.

At present, Cameron is looking for at least 35 Labour MPs to give cast iron guarantees to vote with him on military action, but Downing Street may feel engaging with Benn’s broader strategy offers a superior route to winning broad Commons agreement for a new approach in Syria.

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In his article, Benn writes: “On the question of airstrikes against Isil/Daesh in Syria, it should now be possible to get agreement on a UN security council chapter VII resolution given that four of the five permanent members – the USA, France, Britain and Russia – are already taking military action against Isil/Daesh in Iraq or Syria or in both countries. The prime minister should now be working tirelessly with other countries to try to secure such a resolution.”

For the first time, Benn discusses the possibility that it will not be possible to reach agreement on a chapter VII resolution at the security council, stating: “Of course, we know that any resolution may be vetoed, and in those circumstances we would need to look at the position again.” The wording is designed to imply that Labour recognises its prior support for military action without explicit UN authorisation, such as in Kosovo.

Benn also stresses the absolute necessity of acting, writing: “We have a responsibility to protect people, but in Syria, no one has taken responsibility and no one has been protected. It is the great humanitarian crisis of our age and one of our greatest tests too.”

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He says: “The way we take any decision will matter a great deal. MPs and others may disagree about what the right thing to do is, but we must never forget that we have a responsibility both to help the Syrian people and protect British citizens. Deciding to intervene militarily in another country is one of the most serious decisions parliament can make, but equally, nobody should be in any doubt that inaction is also a decision that will have consequences in Syria.”

So far, safe havens have been rejected by the UK foreign office, and by President Obama. Tobias Ellwood, the Foreign Office minister, told MPs on Monday night: “History tells us that implementing genuinely safe zones is difficult and must be accompanied by an international mandate that would provide the will, the authority and the full means to ensure that they have a chance of being effective. It would also involve significant military commitment. As we have seen, that can be hard to come by from the various parliaments across the world.”