JAKARTA (AFP) - British Prime Minister David Cameron begins a visit to South-east Asia on Monday, seeking greater cooperation in the fight against the Islamic State in Iraq and Syria (ISIS) group and to strengthen trade ties with the region's booming economies.

Cameron will arrive in Indonesia on the first stop of a four-day trip, accompanied by 30 British business leaders and the trade minister, before heading to Singapore, Vietnam and Malaysia.

He will use meetings with President Joko Widodo of Indonesia and Prime Minister Najib Razak of Malaysia to discuss what he has called the "common enemy" of ISIS militants, who have seized vast swathes of territory in Iraq and Syria.

Hundreds of young Britons have joined ISIS in Syria and Iraq, sparking fears they could launch attacks on home soil on their return.

Indonesia, which has the world's largest Muslim population and has long struggled with extremism, fears up to 500 of its citizens have been lured to the Middle East by ISIS, while nationals of Muslim-majority Malaysia have also joined the extremists.

In remarks made before departing for the trip - his first outside Europe since being re-elected in May - Cameron said he would be talking to South-east Asian leaders about "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 against this common enemy," he said.

Britain would offer expertise on "practical counter-terrorism work", he added, and could also learn from Indonesia and Malaysia about what they have done to tackle extremism and build tolerant societies.

MALAYSIA CONTROVERSY

Indonesia has suffered a string of Islamic extremist attacks over the past 15 years, including the 2002 Bali bombings that left 202 people dead.

However, it has been credited with mounting a successful crackdown that dismantled sophisticated militant networks.

Also on the trip are senior figures from prominent British businesses including engine maker Rolls-Royce and construction equipment maker JCB, as the prime minister seeks to drum up trade in the region.

Writing in Britain's Daily Mail newspaper ahead of the visit, Cameron said: "This is a region on the rise, and I'm determined that Britain grabs every opportunity that brings."

However, Cameron could run into controversy during the Malaysian leg of the trip.

He is arriving as Najib battles mounting outrage over allegations that hundreds of millions of dollars were siphoned off from a state-owned development company he launched and retains close links with.

The premier and the company, 1Malaysia Development Berhad (1MDB), have both vehemently denied any wrongdoing. The case is being investigated by Malaysian authorities and a parliamentary committee.

Nurul Izzah, a parliamentarian and daughter of jailed ex-opposition leader Anwar Ibrahim, called for Cameron's entourage to also meet with the opposition.

Meeting only with Najib's government "would be seen as if they were oblivious to the undercurrents here and the public concerns," she told AFP.

On Monday, Cameron will meet with Indonesian leader Widodo as well as the head of regional bloc the Association of South-east Asian Nations.

He departs for Singapore on Tuesday.