MANILA, Philippines (AP) — The Philippines' top diplomat said Thursday he has filed a diplomatic protest after an anchored fishing boat was hit by a suspected Chinese vessel which then abandoned the 22 Filipino fishermen as the boat sank in the disputed South China Sea.

Foreign Secretary Teodoro Locsin Jr. said he filed the protest Wednesday. He disclosed the move in a tweet in response to a suggestion by opposition Sen. Antonio Trillanes IV that an independent investigation be conducted by the International Maritime Organization, a U.N. agency.

Another opposition senator, Risa Hontiveros, called on President Rodrigo Duterte to recall the Philippine ambassador and consuls in China to pressure Beijing to identify and punish the Chinese crewmen allegedly involved in the incident.

China condemned the incident but did not immediately confirm or deny that a Chinese vessel was involved.

The sinking is a delicate development in the long-contested South China Sea, which is seen as a potential flashpoint in Asian relations. Tensions escalated after China converted seven disputed reefs into islands which can serve as forward military bases and intimidate rival claimant states in the strategic waterway, where U.S. forces undertake "freedom of navigation" patrols.

Defense Secretary Delfin Lorenzana disclosed on Wednesday that a boat, identified as F/B Gimver 1, was carrying 22 Filipino fishermen and sank Sunday night after being hit by the suspected Chinese vessel at Reed Bank off the western Philippine province of Palawan.

Lorenzana strongly condemned the crew of the vessel, which he said was identified by the Filipinos as Chinese, for abandoning the fishermen while their boat sank. He thanked Vietnamese fishermen who rescued the Filipinos and brought them to safety.

Asked if he would recommend any action against China, the defense chief told The Associated Press on Thursday, "A strongly worded diplomatic protest is in order."

Duterte's spokesman, Salvador Panelo, said the abandonment of the fishermen was "uncivilized as it is outrageous."

Panelo called on Chinese authorities to investigate and impose sanctions to the Chinese crew.

In Beijing, Chinese foreign ministry spokesman Geng Shuang said the incident "should be condemned" wherever the vessel came from.

Citing information provided by the Philippines, Geng described the sinking as "an ordinary maritime traffic accident" and criticized assumptions made about it. "It is irresponsible to resort to the media to hype and politicize the incident without verification," he said, adding a Chinese investigation was underway in coordination with Philippine authorities.

The Philippine coast guard said it was checking whether those involved were Chinese fishermen or from other neighboring countries such as Vietnam and if the collision was intentional.

As their boat sank, the Filipino fishermen scrambled to smaller boats and were eventually picked up by a Vietnamese fishing boat and then transferred to a Philippine navy ship, Lorenzana said.

The F/B Gimver 1 had been anchored "when it was hit by the Chinese fishing vessel," he said, indicating it may have been rammed.

Philippine officials say Reed Bank lies well within their country's exclusive economic zone, an internationally recognized stretch of water where coastal states have exclusive rights to fisheries, undersea oil and gas deposits and other resources. The Philippines has suspended oil and gas exploration in the area due to past Chinese protests.

An international arbitration tribunal in 2016 upheld the Philippines' sovereign rights over its EEZ and invalidated China's claims to virtually all of the South China Sea. China has refused to recognize the ruling.

In past years, Chinese ships have blocked or intimidated Philippine military and civilian vessels at Reed Bank and nearby Second Thomas Shoal, where Philippine marines keep watch on board a long-marooned Philippine navy ship while being constantly monitored by Chinese coast guard ships in a years-long standoff.

___

Associated Press researcher Liu Zheng in Beijing contributed to this report.