The United States warned Thursday it would not tolerate efforts to control sea and air routes in the South China Sea, as Southeast Asian nations debated how hard to pressure Beijing on its island-building.

US Secretary of State John Kerry said at a regional summit that open navigation of the strategically important area was an "intrinsic right".

"Let me be clear: The United States will not accept restrictions on freedom of navigation and overflight, or other lawful uses of the sea," he told reporters in Kuala Lumpur, after attending a summit dominated by the flashpoint issue.

China has sparked alarm by expanding tiny reefs and constructing military posts, steps viewed by some of its neighbours as violating a regional pledge against provocative actions in the area.

The long simmering dispute has flared at the Malaysia meet, which is being hosted by the 10-nation Association of Southeast Asian Nations (ASEAN) and includes envoys from more than a dozen other nations such as China, Japan, South Korea and the US.

Beijing claims control over nearly the entire South China Sea, a key shipping route thought to hold rich oil and gas reserves.

Vietnam, the Philippines, Malaysia and Brunei -- all ASEAN members -- also have various claims, as does Taiwan, many of which overlap.

Each year the regional ASEAN bloc, which prides itself on its history of consensus diplomacy, releases a joint communique after the annual meeting of its foreign ministers, which took place Tuesday.

But the nations have been at loggerheads for the last three days over the wording of the paragraphs addressing the South China Sea.

Diplomatic sources told AFP that the Philippines and Vietnam in particular were pushing for stronger language on Chinese land reclamation, which could help shore up Beijing's disputed territorial claims.

- Chinese friends -

But there was pushback from traditional China allies among the association, they added.

"China's friends are taking a hard stance," said one diplomat familiar with the drafting.

The diplomat did not specify which countries were taking a hard line, but Cambodia, Laos and Myanmar traditionally ally with China within ASEAN.

The tug-of-war raises the spectre of a 2012 ASEAN meeting hosted by Cambodia, when the bloc was unable for the first time in its four-decade history to issue a joint statement.

Cambodia was accused of precipitating the debacle by refusing to allow criticism of China over its maritime territorial assertions.

"China has already figured out how ASEAN works on the South China Sea, it knows how to divide us. Look at what happened in Cambodia," one diplomat at the talks in Kuala Lumpur told AFP.

Singapore Foreign Minister K. Shanmugam told reporters Thursday morning that the joint statement was supposed to have been completed the previous day.

"It has not been finalised as of now. There are difficulties," he said.

"The paragraphs relating to the South China Sea are causing some problems," he added.

A draft of the communique obtained by AFP makes no mention of halting reclamation.

Instead it warns that recent developments in the sea "have the very potential of undermining peace, security and stability".

Delegates said they still hoped to get a final joint statement by the end of the day.

The United States and Southeast Asian nations have called for a halt to further land-reclamation and construction.

China had so far refused, but on Wednesday Chinese Foreign Minister Wang Yi said land reclamation had "already stopped".

However some delegates in Kuala Lumpur have played down those claims.

One diplomat told reporters: "They're not saying they're stopping construction, nor are they saying they'll stop future reclamation."

At his press conference Kerry told reporters: "The Chinese have indicated that they have stopped. I hope it is true. I don't know yet."