The Philippine Coast Guard said it deployed aircraft on Wednesday to monitor the Chinese research ship Xiang Yang Hong 33 near Iroquois Reef in the Spratly Islands, where it observed the vessel launching a service boat toward the reef.The coast guard said the operation “confirmed ongoing unauthorized marine scientific research activities” within waters over which the Philippines claims sovereign rights and jurisdiction.

Iroquois Reef lies at the southern edge of Reed Bank, an area believed to contain substantial natural gas and oil reserves and long viewed as strategically significant for Manila’s energy security.

During the aerial patrol, Philippine authorities also reported spotting 41 vessels identified as part of China’s “maritime militia” anchored near Iroquois Reef and around Thitu Island, a Philippine-controlled outpost in the Spratlys inhabited by about 400 civilians and home to a recently established coast guard station.“The Philippines has not granted such consent to the People’s Republic of China for any marine scientific research activities in these waters,” the coast guard said in a statement.

It added that the presence of the research vessel alongside the concentration of Chinese maritime militia ships represented “a serious infringement on Philippine sovereign rights and maritime jurisdiction.”China’s embassy in Manila defended the activities, reiterating Beijing’s longstanding claim of “historic rights” over much of the South China Sea and asserting that the islands and reefs concerned were Chinese territory.

The embassy said Chinese research vessels had carried out their missions “in accordance with international law.”The Xiang Yang Hong 33, a research vessel capable of supporting deep-sea submersible operations, departed China more than three weeks ago and has since been tracked near several Philippine-claimed features in the Spratly chain, including Sabina Shoal and Second Thomas Shoal, both recurring flashpoints between the two countries.

Tensions between Beijing and Manila have intensified in recent years as China expanded coast guard, naval and maritime militia deployments across the contested waterway, where competing territorial claims overlap with key shipping lanes and potentially resource-rich seabeds.

China claims nearly the entire South China Sea despite a 2016 ruling by the Permanent Court of Arbitration in The Hague that found Beijing’s sweeping claims had no legal basis under international law. China has rejected the ruling.

Pakistan’s foreign office spokesperson Tahir Andrabi said the crew members, who had been aboard the MV Touska, were flown into Pakistan overnight and would be handed over to Iranian authorities later in the day.

The vessel was seized by U.S. forces in the Gulf of Oman after it refused orders to alter its course during heightened maritime tensions linked to the standoff in the Strait of Hormuz.

Washington has imposed a naval blockade on Iranian ports since last month, part of broader measures amid escalating conflict with Tehran.A spokesperson for the United States Central Command said earlier that the crew had been repatriated to Pakistan, while Iranian media reported that six crew members had already been released and returned to Iran last week.

Andrabi said the vessel would also be moved to Pakistani territorial waters for repairs before being returned, with coordination involving both U.S. and Iranian authorities. He added that Islamabad welcomed the step and would continue efforts to facilitate dialogue.

The transfer comes as Pakistan positions itself as a mediator between Washington and Tehran. Deputy Prime Minister and Foreign Minister Mohammad Ishaq Dar held talks with Iranian Foreign Minister Seyed Abbas Araghchi on Sunday to discuss regional developments and diplomatic efforts.

Pakistan has hosted discussions between the two sides since February, though recent attempts at negotiations have not yielded a breakthrough. Tensions have remained high, particularly over control of the Strait of Hormuz, where the U.S. has announced plans to escort commercial vessels in an operation it describes as humanitarian.