US President Barack Obama said summit meetings among world leaders this weekend in the Malaysian capital of Kuala Lumpur will focus on the global fight against Islamic State militancy and on the disputed South China Sea.

Speaking to reporters after meeting with Malaysian Prime Minister Najib Razak, Obama said: "Malaysia is part of the coalition to fight (Islamic State) and can be extraordinarily helpful on issues like countering the destructive and perverse narrative that's developed."

Malaysia deployed extraordinary security measures around Kuala Lumpur on Friday as leaders from 18 countries arrived for a pair of weekend summits amid fresh attacks by Islamist militants.

Malaysia's police chief cited unconfirmed reports of an "imminent terrorist threat" in the country, following last week's attacks in Paris and the downing of a Russian airliner over Egypt by Islamic State militants.

Some 4,500 soldiers were deployed or on standby to secure the summit, in addition to thousands of police who have fanned out around the Kuala Lumpur City Centre.

In addition to Obama, leaders from China, Japan, Russia, India, South Korea, Australia and New Zealand are attending the East Asia Summit following the annual Association of Southeast Asian Nations (Asean) meeting.

Obama promised students at a town hall meeting at a Kuala Lumpur University that he would raise concerns about corruption and Malaysia's crackdown on dissent in his meeting with Najib. Critics have accused Najib of escalating a crackdown on dissent and free expression after losing the popular vote in the 2013 general election.