President Rodrigo Duterte delivers a speech in Davao City on Tuesday. Robinson Ninal, Malacañang Photo

MANILA - The United Nations may impose economic sanctions against the Philippines if President Rodrigo Duterte arrests International Criminal Court officials looking into his anti-narcotics drive, a former envoy warned Sunday.

Duterte last week said he will arrest ICC's chief prosecutor Fatou Bensouda as he warned her to stay away from the Philippines.

Bensouda launched in February a preliminary investigation into allegations that Filipino police were murdering thousands of drug suspects, prompting Manila last month to withdraw from the Hague-based tribunal.

If Bensouda is arrested, the ICC may seek the help of the UN Security Council, which can then "impose or recommend economic sanctions... or the use of force--but that is [for] very extreme cases", said Lauro Baja, former Philippine Permanent Representative to the UN.

Baja noted that any withdrawal from the ICC would only take effect a year after notice to the UN, which technically means that the Philippines is still under the tribunal's jurisdiction.

The jurisdiction, however, will "greatly depend also on the cooperation of the government concerned," as the ICC has no enforcement powers and would need backing from the UN Security Council or another body, he said.

"I hope the rhetoric from both sides -- from the President and the ICC persons -- could simmer down, could de-escalate because the more we utter pronouncements of extreme thoughts and measure, e lalong lalala iyan (would worsen the situation)," Baja told DZMM.

He urged Duterte's Cabinet to engage in back channel talks with the ICC, given that the court has not found basis for any coercive action against the Philippines.

The ICC's preliminary probe, Baja added, only determines if there is basis to conduct a formal investigation into the allegations against the President.

Philippine police say they have killed roughly 4,000 drug suspects who fought back during arrest. Rights groups claim the actual number is 3 times higher, accusing authorities of murder.

In the face of international criticism of its drugs war, Manila has described its withdrawal from the ICC as a "principled stand against those who would politicize and weaponize human rights".

The ICC has urged Manila to reconsider its decision, while warning that the move does not prevent the tribunal from continuing its investigation into the killings.

"You, Ms Fatou, do not come here because I will bar you," Duterte had said.

"Not because I am afraid of you (but) because you will never have jurisdiction over my person, not in a million years."

The ICC opened in 2002 to try abuses in countries where national courts cannot or will not prosecute.

Manila ratified the Rome Statute that created the treaty in 2011, but Duterte has insisted it cannot be enforced in the Philippines on a technicality.

Buoyed by high domestic popularity ratings, Duterte has fiercely defended his drug war as a battle to provide security for the nation's 100 million people.

With a report from Agence France-Presse