Asia-Pacific leaders held "robust" talks on the South China Sea at a summit Saturday despite objections by Beijing, a senior US administration official said, in a major diplomatic coup.

The Chinese government had insisted that the issue of the strategically vital South China Sea, which it claims in full, should be off-limits at the meeting of 18 nations on the Indonesian island of Bali.

But Chinese Premier Wen Jiabao was "very measured" at the meeting and did not go on "a tirade" the official said.

The talks came at the end of a week-long drive by President Barack Obama to assert US influence in the Pacific, including sending Marines to Australia and pushing for a trade pact, that has irked China.

Speaking aboard Air Force One, the US official said that at the two-hour leaders' retreat, "the bulk of the discussions were a very robust conversation on maritime security and the South China Sea".

Almost all the leaders addressed maritime security in some form, he said, "and most of them talked specifically about the South China Sea".

Obama was "encouraged" by the talks, he added, which had a "constructive" tone and were "not a shootout at the OK Corral".

He told the meeting the US was not a claimant in the dispute and did not take sides but was involved, the official said, "as a resident Pacific power, as a maritime nation, as a trading nation, and as a guarantor of security in the Asia Pacific region".

Wen, the official said, "started off maybe a little bit grouchy, (but) by and large it was very measured and interesting.

"He was not on a tirade, and he did not use many of the more assertive formulas that we frequently hear from the Chinese, particularly in public."

Wen said China wanted to reach a code of conduct for the sea, and did not qualify the statement as Beijing had in the past, nor did he say that disputes should be resolved in one-on-one negotiations -- China's longstanding position.

Russian foreign minister Sergei Lavrov and Indonesian President Susilo Bambang Yudhoyono, the chairman of the meeting, specifically said maritime security should be discussed by the summit, the official said.

"The Chinese will come away from the meeting believing that a heavy-handed approach on the South China Sea will backfire badly and that there is a genuine consensus on the importance of a constructive process to find a peaceful way forward," the official said.

"If these sorts of indications are reliable bellwethers to the direction that China is moving, it would be a positive thing."