The Philippines said on Thursday that China wants to survey potentially resource-rich seas off the country’s northeast coast but Manila will agree only if a Filipino scientist is allowed to observe.

Acting Foreign Secretary Enrique Manalo told ABS—CBN News Channel that a number of Chinese requests to survey Benham Rise have been denied because China rejected that condition.

Some requests are still pending.

Defense Secretary Delfin Lorenzana has said that Chinese survey ships were spotted crisscrossing the Benham Rise area from July to December last year.

It was not clear what the ships were doing. Chinese officials have said their ships have the right of innocent passage through the area.

Benham Rise is on the opposite side of the Philippines from where the countries are locked in a dispute over ownership of islands and shoals in the South China Sea.

The UN Commission on the Limits of the Continental Shelf confirmed in 2012 that Benham Rise is part of the extended continental shelf of the Philippines, where it has sovereign rights to explore and exploit oil, gas and other mineral resources, including sedentary species.

Mr. Manalo said after the Chinese ships’ presence in Benham Rise was reported the Department of Foreign Affairs sent a diplomatic note to China to inquire what they were doing there.

“China replied that number one, they fully respect and recognize sovereign rights of the Philippines on Benham Rise and secondly, it is not an area under dispute,” he said, adding they were satisfied with their explanation.

“This was confirmed two or three times so the implication is they will follow the rules laid out by UNCLOS and that’s how we are going to deal with this issue,” he added, referring to the United Nations Convention on the Law of the Sea.

On Wednesday, National Security Adviser Hermogenes Esperon told a Senate hearing that a Chinese ship seen in the area conducted research but the Philippines has no indication as of now that it surveyed what’s on the seabed.

It also could not be established if the research was done inside or outside the country’s exclusive economic zone, he added.

The status of Benham Rise was raised in an affidavit submitted on Thursday to supplement an impeachment complaint filed against President Rodrigo Duterte.

The original complaint says Mr. Duterte should be impeached because of the thousands of deaths in his anti-drug crackdown and alleged corruption.