KUALA LUMPUR (REUTERS) - United States President Barack Obama arrived in Malaysia on Friday (Nov 20) on the final leg of a series of summits aimed at furthering Washington's bid to rebalance ties towards Asia and challenge China's increasingly assertive posture in the region.

Security was unusually tight in the Malaysian capital with police citing unconfirmed reports of an "imminent terrorist threat", following last week's attacks in Paris and the downing of a Russian airliner over Egypt by Islamic State in Iraq and Syria (ISIS) militants.

Mr Obama is joining leaders of the 10-member Asean for a weekend summit. Leaders from seven other countries with close partnerships with the grouping - Australia, China, India, Japan, New Zealand, Russia and South Korea - will also attend a series of meetings starting on Saturday.

At least 2,000 army personnel were stationed at strategic points in Kuala Lumpur and another 2,500 were on standby, Armed Forces chief Zulkifeli Mohd Zin said.

Mr Obama and most of the other leaders are arriving from the Asia Pacific Economic Cooperation (Apec) summit in Manila, where the US President tried to turn the heat on China over its territorial claims in the disputed South China Sea.

Both the Apec meeting and the Asean summit typically focus on economic issues but have been overshadowed by global efforts to combat ISIS following the attacks in Paris that killed at least 129 people.

Mr Obama's has tried to emphasise the U.S. "rebalance" towards the Asia-Pacific with his signature Trans-Pacific Partnership trade deal and strengthening ties with Asian nations facing a more muscular China. But he has been dogged during his swing through the region by concerns over how to counter Islamic State militants blamed for the Paris attacks.

Much of his time at the G-20 summit in Turkey and the Apec gathering in Manila was focused half a world away on the chaos and violence emanating from Syria's 4.5-year-old civil war.