The Philippine government has summoned the Chinese ambassador to press its demand for Chinese vessels to immediately leave a reef claimed by Manila in the South China Sea.

Officials said that the Chinese vessels’ presence is stoking tensions in the area.

The escalating feud between Manila and Beijing started after more than 200 Chinese vessels suspected by Philippine authorities to be operated by militias were spotted early last month at Whitsun Reef

The Philippine government demanded the departure of the vessels before deploying coast guard and patrol boats to the area, but China said it owns the reef and explained that Chinese vessels were sheltering from rough seas.

After summoning Ambassador Huang Xilian on Monday, Philippine foreign under-secretary Elizabeth Buensuceso expressed to him Manila’s “displeasure over the illegal lingering presence of Chinese vessels around Julian Felipe Reef”, the foreign affairs department said.

The Julian Felipe Reef is the Philippine name for Whitsun Reef in the hotly disputed Spratlys region of the busy waterway.

“The continuing presence of Chinese vessels around the reef is a source of regional tension,” Ms Buensuceso said.

She reiterated to Mr Huang that the reef, which lies about 175 nautical miles west of the Philippine province of Palawan, is within an internationally recognised offshore zone where Manila has the exclusive right to exploit fisheries, oil, gas and other resources.

Ms Buensuceso also cited a 2016 ruling in an international arbitration case the Philippines brought against China that invalidated Beijing’s vast claims on historical grounds to virtually all of the South China Sea under a 1982 UN maritime treaty.

The Philippine military has said aerial surveillance showed some of the Chinese vessels have left the reef, but more than 40 remained moored in the area in late March.

It debunked China’s claim that the vessels were sheltering from rough seas, saying the weather has been fine around the reef.

The United States has said it would stand by the Philippines amid the stand-off.

The department of national defence in Manila said last week that the Philippines could seek the help of the US, with which it has a mutual defence treaty, to protect its interests in the South China Sea.

The Philippines’ high-profile protests against China over Whitsun has unfolded amid cosier relations President Rodrigo Duterte nurtured with China after taking office in mid-2016.

Mr Duterte has been repeatedly criticised for not immediately demanding Chinese compliance with the 2016 arbitration ruling and taking a stronger stand against China’s actions in the disputed waters.

The Spratly chain of islands, islets and atolls are claimed entirely or partly by China, the Philippines, Vietnam, Malaysia, Taiwan and Brunei.

China has turned seven disputed reefs into missile-protected island bases in recent years, ratcheting up tensions in what has long been feared as a potential flashpoint in Asia.