The Philippine government announced Tuesday a new diplomatic protest against China over disputes in the South China Sea, a long-thorny issue that has flared anew as the next Philippine president prepares to take office next month.

The Philippines has filed hundreds of diplomatic protests against Beijing in recent years for what it considers acts of aggression in the disputed waters, despite improved ties between Beijing and Manila under outgoing President Rodrigo Duterte, whose six-year term ends on June 30.

The territorial conflicts are among the key challenges President-elect Ferdinand Marcos Jr. will face when he takes office after his landslide electoral victory on May 9. He has said he will use diplomatic means with China over the issue, the same approach adopted by Duterte, who has been criticized for not taking a more aggressive stance against Beijing’s increasingly assertive actions in the resource-rich and busy waterway.

The Department of Foreign Affairs said Tuesday it filed a diplomatic protest over China’s imposition early this month of an annual fishing ban lasting three and a half months that covers areas in the disputed waters where "the Philippines has sovereignty, sovereign rights and jurisdiction."

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It said the ban is not limited to Chinese fishing vessels and violates the 1982 U.N. Convention on the Law of the Sea and a 2016 arbitration tribunal’s decision that invalidated Beijing’s vast historic claims in the strategic waterway and upheld the Philippines’ sovereign rights in a stretch of coastal waters called its exclusive economic zone.

China does not recognize the arbitration ruling and continues to defy it.

The Chinese ban "has no basis in law, and undermines the mutual trust, confidence, and respect that should underpin bilateral relations," the department said in a statement.

Chinese structures in South China Sea

Chinese structures and buildings on the man-made Fiery Cross Reef at the disputed Spratlys group of islands in the South China Sea are seen on March 20, 2022. The Philippine government has summoned a senior Chinese diplomat in Manila to protest the harassment by the Chinese coast guard of a research vessel manned by Filipino and Taiwanese scientists in the disputed South China Sea, officials said Tuesday May 31, 2022. (AP Photo/Aaron Favila) (AP)

"The Philippines calls on China to comply with its obligations under international law" and "cease and desist from the conduct of illegal actions," including its "annual practice of declaring a fishing ban over areas that extend far beyond China’s legitimate maritime entitlements," it said.

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Separately, Philippine foreign affairs officials said late Monday that the department summoned a Chinese diplomat in early April to protest alleged harassment by the Chinese coast guard of a research vessel in the South China Sea.

They said they were reviewing other recent violations of Philippine rights in Second Thomas Shoal and Reed Bank, which lie within Manila’s exclusive economic zone but which China also claims, before taking further diplomatic action.

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The department said it summoned a Chinese Embassy official in Manila to protest the "harassment by the Chinese coast guard" of research vessel R/V Legend, which was undertaking a survey of undersea fault lines along the Manila Trench west of the northern Philippines.

Philippine diplomats did not provide other details, but people involved in the scientific research told The Associated Press last month that a Chinese coast guard ship shadowed R/V Legend, which was carrying five Filipino scientists and an unspecified number of Taiwanese counterparts, from March 25 to 30.

Chinese military exercise in South China Sea

In this photo released Dec. 31, 2021, by Xinhua News Agency, an undated photo shows a carrier-based J-15 fighter jet preparing to land on the Chinese navy's Liaoning aircraft-carrier during open-sea combat training. China is holding military exercises in the disputed South China Sea coinciding with U.S. President Joe Biden's visits to South Korea and Japan that are largely focused on countering the perceived threat from China. (Hu Shanmin/Xinhua via AP) (Hu Shanmin/Xinhua via AP)

A Chinese coast guard ship maneuvered about 2 to 3 nautical miles (3 to 5 kilometers) from the R/V Legend, causing concern among the scientists because the research vessel was towing a long survey cable in the sea, said Carla Dimalanta of the National Institute of Geological Sciences at the University of the Philippines.

The offshore survey, which was scheduled to end April 13, was a joint project of the Philippine institute and the National Central University in Taiwan and aimed to help map offshore faults and other geologic features that could set off earthquakes, tsunamis and other hazards. The research was partly funded by the Philippine Department of Science and Technology, she said.

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The Filipino scientists reported the incident to the Philippine government, which deployed a coast guard patrol ship, the BRP Capones, to keep watch on the research vessel, the coast guard in Manila said last month.

China, the Philippines, Vietnam, Taiwan, Malaysia and Brunei have been locked in a tense territorial standoff in the busy waterway for decades.

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In past years, the Philippines has protested the Chinese coast guard’s blocking of Filipino supply ships en route to Second Thomas Shoal, where Filipino marines stand watch on a long-marooned navy ship. Chinese ships have also disrupted Philippine vessels exploring for undersea oil and gas in Reed Bank, Philippine officials said.