David Cameron is to urge closer counter-terrorism co-operation with South East Asian states amid fears that Islamic State is trying to gain a foothold in the region.
The Prime Minister is heading to Indonesia on the first stop of a four-day tour intended to drum up trade for Britain.
But he will also use meetings with President Joko Widodo in Jakarta and later Prime Minister Najib Razak of Malaysia to raise the threat from the extremists.
IS – also known as Isil and Daesh - and other terror groups have been pumping out propaganda in local languages, and their support is thought to be growing.
Around 500 people from Indonesia – which has the world's largest Muslim population – and 200 from Malaysia are thought to have joined IS in Iraq and Syria.
Mr Cameron will offer more practical counter-terrorism co-operation to the countries, such as disrupting foreign fighters and improving aviation security.
The premier, who delivered a keynote speech on tackling radicalisation earlier this month, is also planning to gather information about how they are tackling the extremist narrative and explore whether the UK can learn from their approach.
Speaking ahead of his departure for Indonesia, Mr Cameron said: "Isil is one of the biggest threats our world has faced.
"We will only defeat these brutal terrorists if we take action at home, overseas and online and if we unite with countries around the world unite against this common enemy.
"Last Monday, I set out what more we need to do at home to tackle this extremist ideology and build a stronger, more cohesive society. This week, I'll be talking to leaders in South East Asia about what they're doing to keep their country safe from these Islamist extremists.
"All of us face a threat from foreign fighters and from increasing radicalisation within our countries and it's right that we look at what help we can provide to one another.
"I think Britain can offer expertise on practical counter-terrorism work – dealing with the threat from foreign fighters and investigating potential terrorist plots.
"And I think Britain can learn from Indonesia and Malaysia on the work they have done to tackle the extremist ideology and to build tolerant and resilient societies."