US Secretary of State Antony Blinken told south-east Asian leaders on Friday that the US is concerned about China’s “increasingly dangerous and unlawful” activities in the disputed South China Sea during an annual summit meeting.

He also pledged the US will continue to uphold freedom of navigation in the vital sea trade route.

The 10-member Association of South-east Asian Nations’ (Asean) meeting with Blinken followed a series of violent confrontations at sea between China and Asean members Philippines and Vietnam, which have fuelled concerns that China’s increasingly assertive actions in the waterways could spiral into a full-scale conflict.

China, which claims almost the entire sea, has overlapping claims with Asean members Vietnam, the Philippines, Malaysia and Brunei, as well as Taiwan.

About a third of global trade transits through the sea, which is also rich in fishing stocks, gas and oil.

Beijing has refused to recognise a 2016 international arbitration ruling by a UN-affiliated court in the Hague that invalidated its expansive claims, and has built up and militarised islands it controls.

“We are very concerned about China’s increasingly dangerous and unlawful activities in the South China Sea which have injured people, harm vessels from Asean nations and contradict commitments to peaceful resolutions of disputes,” said Mr Blinken, who is filling in for President Joe Biden, in his opening speech at the US-Asean summit.

“The United States will continue to support freedom of navigation, and freedom of overflight in the Indo Pacific.”

The US has no claims in the South China Sea, but has deployed navy ships and fighter jets to patrol the waters in a challenge to China’s claims.

Chinese and Philippine vessels have clashed repeatedly this year, and Vietnam said last week that Chinese forces assaulted its fishermen in the disputed sea.

China has also sent patrol vessels to areas that Indonesia and Malaysia claim as exclusive economic zones.

The US has warned repeatedly that it is obligated to defend the Philippines – its oldest treaty ally in Asia – if Filipino forces, ships or aircraft come under armed attack, including in the South China Sea.

Philippine President Ferdinand Marcos Jr complained to summit leaders on Thursday that his country “continues to be subject to harassment and intimidation” by China.

He said it was “regrettable that the overall situation in the South China Sea remains tense and unchanged” due to China’s actions, which he said violated international law.

He has called for more urgency in Asean-China negotiations on a code of conduct to govern the South China Sea.

Singaporean leader Lawrence Wong earlier this week warned of “real risks of an accident spiralling into conflict” if the sea dispute is not addressed.

UN secretary-general Antonio Guterres, who held a separate meeting with Asean leaders, expressed deep concern about the worsening crisis in Myanmar, and urged Asean to co-operate with the UN special envoy to find a breakthrough.

He said a third of Myanmar’s population are in dire need of humanitarian assistance, with almost 3.5 million people displaced by a civil war since the army ousted an elected government in 2021 and refused to comply with an Asean peace plan.