WASHINGTON (REUTERS) - South-east Asian leaders have accepted an invitation from US President Barack Obama to meet for a summit in the Californian resort of Sunnylands early next year, a spokesman for the White House's National Security Council said on Wednesday.

Obama extended the invitation to the leaders of the 10-nation Association of South-east Asian Nations during a visit to Asia last month.

"The President is pleased the leaders have accepted his invitation to gather at Sunnylands, in early 2016," Myles Caggins, an NSC spokesman, said.

Caggins declined to provide a specific timing for the summit.

Japan's Kyodo news agency on Monday quoted an Asean official source as saying the summit was expected to be held Feb 15-16.

Diplomats from two Asean countries said they understood this to be the timing, but it had yet to be confirmed.

The United States is keen to promote Asean unity in the face of increasingly assertive behaviour by China in pursuit of territorial claims in the South China Sea.

Four Asean members - Brunei, Malaysia, Singapore and Vietnam - are also part of the 12-nation Trans-Pacific Partnership trade pact, which is the key economic plank of Obama's economic and security pivot to Asia in response to China' growing power.

The choice of Sunnylands is symbolic as the Rancho Mirage retreat there was the venue of an informal meeting between Obama and Chinese President Xi Jinping in 2013 that sought to chart a new way forward in US-China relations but did little to ease tensions.