British Prime Minister David Cameron is urging closer counter-terrorism co-operation with South East Asian states amid fears that Islamic State is gaining a foothold in the region.

Cameron 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 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.

Cameron will offer more practical counter-terrorism co-operation to the countries, such as disrupting foreign fighters and improving aviation security.

Speaking ahead of his departure for Indonesia, Cameron said IS 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.

"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."