FOREIGN AFFAIRS Secretary Teodoro L. Locsin Jr. retracted his earlier threat to ban Chinese survey ships from waters covered by the country’s exclusive economic zone, saying an international treaty bars the Philippines from doing so.

“I am reliably informed that under UNCLOS we cannot ban marine surveys but that marine surveys need our permission to be conducted,” Mr. Locsin said on Twitter on Tuesday, referring to the United Nations Convention on the Law of the Sea.

He said the Philippines would apply the law uniformly on all neighbors such as the US, France, Japan and China.

Earlier yesterday, presidential spokesman Salvador S. Panelo said the palace agrees with Mr. Locsin’s move to ban Chinese survey ships, which becomes the policy of the Duterte administration “unless the president makes another policy statement.”

Ryan Martinson, an assistant professor at the US Naval War College, said in a Twitter post on Aug. 6 that the Chinese oceanographic survey ship Zhanjian had been seen operating 80 nautical miles off the Philippine east coast.

On Aug. 7, he also tweeted: “Add the Dong Fang Hong 3 to the list of Chinese survey ships operating in the Philippines’ exclusive economic zone today.”

In a radio interview last Sunday, Mr. Panelo said the Philippine government could seek US help in monitoring the country’s exclusive economic zone.

Responding to Mr. Panelo, Mr. Locsin tweeted: “I banned marine survey ships, amending restriction to France and Japan by adding China.”

“To pick and choose invites suspicion of favoritism,” the Foreign Affairs chief said then. “I will universalize the ban. Period. Granting exception to one country will automatically lift the ban universally. Exceptions invite bribes,” he added.

Jay L. Batongbacal, director of University of the Philippines Institute of Maritime Affairs and Law of the Sea, replied to Mr. Locsin’s Tweet: “Sir, could we please allow at least Philippine marine scientific research to push through?”

He said UP had organized marine scientific research but got banned after inviting foreign scientists and asking to use foreign ships. “We end up losing opportunities for tech transfer and experience.”

Mr. Locsin said he wanted to “see the academic qualifications of the UP guys looking for a cruise.”

President Rodrigo R. Duterte earlier said he plans to invoke a 2016 ruling by an international arbitration panel in the Hague that rebuffed Chinese claims over parts of the South China Sea when he visits Beijing later this month, according to Mr. Panelo.

The United Nations tribunal in July 2016 ruled China’s efforts to assert control over the South China Sea exceeded the law, rejecting its shared claims with Taiwan to more than 80% of the main waterway.

China has rejected the ruling. — Arjay L. Balinbin