Labour has signalled that it is prepared to support RAF air strikes on Islamic State in Syria provided that ministers set out an effective case for military action.
Shadow defence secretary Vernon Coaker said ministers needed to demonstrate that any further UK intervention had the support of other countries in the region as well as a proper legal basis.
In the wake of the Tunisia beach terror attack, Defence Secretary Michael Fallon pointed to the "strong case" previously made by the Government for extending air strikes against Islamic State (IS) – also referred to as Isil - into Syria.
He stressed however that ministers would not press for a fresh parliamentary mandate for military action unless it was clear that there was "sufficient consensus" among MPs.
In the Commons vote last September, the Government confined the motion to authorising air strikes against IS in Iraq in the face of opposition from Labour as well as some Tory MPs to including Syria as well.
However, in a change of policy, Mr Coaker said that Labour would "carefully consider" any fresh proposals that the Government brought forward, while setting out the terms on which it would give its support.
"We all need to be clear about what difference any action would make to our objective of defeating Isil, about the nature of any action, its objectives and the legal basis," he said.
"Any potential action must command the support of other nations in the region, including Iraq and the coalition already taking action in Syria.
"This is a time for a considered assessment of the best course of action we can take to defeat this deadly threat to the UK, an objective that unites us all."