MANILA — The Philippines must secure Senate approval before rejoining the International Criminal Court, Sen. Ronald "Bato" dela Rosa said on Monday, after President Ferdinand Marcos Jr. indicated the possibility of the country's return to the tribunal.

"If you want to rejoin, dadaan pa rin 'yan sa proseso," said Dela Rosa, a former police chief who led President Rodrigo Duterte's drug war that the ICC is investigating.

"After the president's ratification, it has to be concurred by the Senate by a two-thirds vote. So that’s the process. Back to zero back to square one," he told ANC's "Headstart."

Dela Rosa said failure to follow that process would be unconstitutional. When asked if the Senate would concur with the return to ICC, he replied, "I don't think so."

"The Senate is composed of 24 independent republics. Nobody can dictate these 24 independent republics sa isang… one stroke mapa-oo mo, mahirap," he said.

Marcos last week said the Philippines was studying a possible return to the International Criminal Court, which is investigating the Duterte administration's war on drugs.

"Should we return under the fold of the ICC? So that is again under study. So we’ll just keep looking at it and see what our options are," Marcos said.

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• Marcos says Philippine return to ICC 'under study'

But the President also reiterated that it was not right for foreign bodies to dictate to the Philippines who should be investigated or arrested. Dela Rosa said he was holding on to this remark by Marcos.

"It remains a possibility. But very clear 'yung sinabi ng ating Pangulo that hindi kailangan, hindi dapat makialam ang ICC. Hindi kailangan na tagalabas pa, mga banyaga pa ang magsabi sa ating pulis kung sino dapat ang hulihin, sino ang dapat arestuhin, sino dapat ang ikulong," Dela Rosa said.

"We have to respect the decision of the President not allowing ICC to come back."

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Duterte pulled the Philippines out of the ICC in 2019, a year after the Hague-based tribunal began a preliminary probe into his narcotics crackdown.

At least 6,181 people were killed in more than 200,000 anti-drug operations, according to the latest official data released by the Philippine government.

ICC prosecutors estimate the death toll at between 12,000 and 30,000.

— With a report from Agence France-Presse