US President Barack Obama met his Russian counterpart Vladimir Putin three times on the sidelines of an Asia-Pacific summit on Tuesday, with their conversations covering Iran, Syria and Ukraine, the White House said.

Relations between Washington and Moscow are at their lowest since the Cold War, with Russia under US-backed Western sanctions over its seizure of the Crimea this year and its role in the separatist war in eastern Ukraine.

But the two spoke for "a total of approximately 15-20 minutes" during the Asia-Pacific Economic Cooperation (APEC) gathering at a lakeside venue north of the Chinese capital, National Security Council spokesperson Bernadette Meehan told reporters.

"Their conversations covered Iran, Syria, and Ukraine," she said.

Both Russia and the US are involved in the P5+1 talks on Iran's nuclear programme, but on Syria Moscow is a key ally of Bashar al-Assad's government and has supported him throughout the uprising that began in March 2011.

Washington last year threatened military action against the Syrian regime, but eventually settled for a deal that saw Damascus give up its chemical weapons arsenal.

The biggest current differences between the US and Russia, though, are over Ukraine.

In mid-October, Putin accused Obama of having a hostile attitude towards Russia, while Obama decried "Russian aggression in Europe" in a recent speech to the United Nations General Assembly.

Earlier in the day deputy national security adviser Ben Rhodes told reporters in Beijing: "We continue to be deeply troubled by Russian activities. If they continue... it's a recipe for isolation."