US Secretary of State Hillary Clinton warned Monday against coercion in the conflict-riven South China Sea and voiced hope that Beijing would find a peaceful resolution with Southeast Asian nations.

With tensions mounting in recent months between China and other claimants to the strategic waterway, Clinton on a visit to Indonesia declared anew that the United States found a "national interest" in ensuring freedom of navigation.

Clinton, who heads Tuesday to Beijing, did not criticise China directly but voiced clear unease over the fast-growing Asian power's recent establishment of a remote garrison in the sea hotly disputed among six states.

"The United States believes very strongly that no party should take any steps that would increase tensions or do anything that would be viewed as coercive or intimidating to advance their territorial claims," Clinton said.

"We believe the nations of the region should work collaboratively together to resolve disputes without coercion, without intimidation, without threats and certainly without the use of force," Clinton said.

Clinton, speaking at a news conference with Indonesian Foreign Minister Marty Natalegawa, urged progress on a code of conduct to manage the overlapping disputes, warning that a "miscalculation" could escalate the situation in the tense waters.

During Clinton's last visit to the region in July, foreign ministers of the 10-member Association of Southeast Asian Nations, or ASEAN, failed to reach a consensus that would allow them to negotiate jointly with China.

Clinton praised a subsequent declaration by the ASEAN foreign ministers, led by Natalegawa, who recommitted to a peaceful resolution of disputes and to a unified position on a code of conduct.

Clinton, who will become the first US secretary of state to visit all ASEAN nations when she stops in Brunei later this week, expressed optimism that the elusive code of conduct could come closer to reality in time for a November summit to be attended by President Barack Obama.

"I think we can make progress before the East Asia Summit and it's certainly in everyone's interest that we do so," she said.

The Indonesian foreign minister voiced support for ASEAN unity and said that the overlapping claims in the South China Sea "must be resolved peacefully".

But Natalegawa, who last month welcomed Chinese Foreign Minister Yang Jiechi to Jakarta, said that the diplomatic efforts should not be seen as targeting Beijing.

"It's important to underscore ASEAN unity is not meant to be at the expense of any other party. It's not about us rallying around to counter or to put any other country on the spot," he said.

The Philippines and Vietnam have both accused China of an intimidation campaign over territorial disputes in the South China Sea, a waterway through which half of the world's cargo sails.

But several Southeast Asian nations including Cambodia have close ties with China and have been less enthusiastic about taking a hard line.

In a show of support for ASEAN, Clinton will on Tuesday visit the bloc's headquarters in Jakarta and meet its secretary-general, Surin Pitsuwan.

Ahead of the talks, Surin cautioned that too much attention on the issue could prove counterproductive.

He said: "We just hope that all the attention and the concern would not add to the fragility and instability over the issue. We want a conducive environment that would enable us to achieve the COC as soon as possible.

"As a major dialogue partner, the US certainly has a role to play and a contribution to make."

China agreed in 2002 to negotiate with ASEAN on a code of conduct but since then Beijing has preferred to deal with each nation individually and has repeatedly warned the United States against trying to "contain" its clout.

Obama, who spent part of his childhood in Indonesia, took office with a mission to expand relations with the world's largest Muslim-majority nation, seeing it as an ideal partner due to its embrace of democracy since the 1990s and historically moderate brand of Islam.

But momentum for closer relations has faltered, in part due to concern in the United States over recent mob violence by Indonesian Islamists against minorities.

Clinton gingerly raised concerns at her news conference, saying: "The world looks to Indonesia as the leading democracy in the region and being the third largest democracy in the world to promote democracy and human rights.

"We both agree strongly that there should be no discrimination against minorities on any basis -- religious or communal, sectarian, ethnic -- and that we should promote freedom and tolerance for all," she said.