The US secretary of state has committed Washington to aiding the Philippines in the event of an “armed attack” on its vessels or aircraft in the disputed South China Sea, in what some see as a warning shot to China.

Speaking in Manila after meeting the president, Rodrigo Duterte, Mike Pompeo told the Philippines: “We have your back” and invoked the two countries’ mutual defence treaty.

“Any armed attack on any Philippine forces, aircraft or public vessels in the South China Sea will trigger mutual defence obligations under article IV of our mutual defence treaty,” Pompeo said.

The South China Sea is one of the most contested patches of water in the world, with Brunei, China, Malaysia, the Philippines, Taiwan and Vietnam with overlapping claims in the region.

Pompeo is the first US official to openly affirm the US’s military commitment to defending Philippine sovereignty over the South China Sea.

In 2016 the Philippines won an international arbitration case against China’s claim over practically the entire South China Sea, which is rich in both fish and potential oil and gas reserves and is a valuable trade route. But China did not recognise the ruling and has continued to militarise the sea by building vast fortresses, with control towers, airstrips and helipads, on reclaimed sand islands.

Pompeo told his Philippine hosts that China’s island building and military activities in the South China Sea “threaten your sovereignty, security and therefore economic livelihood, as well as that of the United States”.

His statement comes two months after the Philippine defence secretary, Delfin Lorenzana, expressed an intent to review the treaty, precisely because of its unclear provisions and a lack of concrete commitment from the US to come to its aid if the South China Sea dispute turns into an armed clash with China.

Lorenzana told reporters on Friday he still wanted a review of the treaty, however, “to get all ambiguities cleared and put in paper as part of the treaty”.

The Philippines was once one of the boldest critics of China’s claim over the South China Sea. However, under Duterte Manila has mostly put the territorial dispute to the side, opting for expanded economic and trade links, which some critics have described as a defeatist attitude by the Philippine president.



In response to Pompeo’s remark, at a news conference in Beijing, Lu Kang, a spokesman for the ministry of foreign affairs, said there was “nothing to be worried about” and the situation in the South China was increasingly stable.



However, he warned that the US should “not make trouble out of nothing”.



“If outside countries like the US truly consider the peace, stability and welfare of local residents, they should not make waves when there is no wind,” he said. “A country’s own government and people understand better than any other countries what their own advantages are.”