Foreign ministers from 21 countries are meeting in London to discuss ways to co-ordinate their efforts to combat the jihadist group Islamic State (IS).
IS controls large swathes of Syria and Iraq and the US-led coalition has been carrying out air strikes since August.
But UK Foreign Secretary Philip Hammond insisted much more needed to be done.
He told the BBC that the countries wanted to find ways to halt the flow of recruits to IS, cut off its funding and “tackle the underlying narrative”.
They will also look at providing more military assistance to those fighting IS on the ground, and more humanitarian aid to its victims.
BBC diplomatic correspondent James Robbins says the recent attacks by Islamist militants in France have put even greater political pressure on governments to show decisive results.
At the start of Thursday’s conference at Lancaster House, which he is co-hosting with Mr Hammond, US Secretary of State John Kerry told reporters: “We still have a lot of work to do.”
“The purpose of coming here is to bring everybody’s best advice, everybody’s thoughts about where there may be weaknesses, everybody’s thoughts about things we can do better, put that together and lay down the strategy for the days ahead.”
A senior US state department official said foreign fighters would be the “real focus” of the London conference, and that an expert working group would be formed to discuss sharing information to stop them travelling.
The European police agency, Europol, estimates that up to 5,000 EU citizens have travelled to Syria and Iraq to fight. Thousands of others have travelled from Arab and Muslim states.