MANILA — The Philippine Congress on Wednesday approved a request from President Rodrigo Duterte to extend martial law on the southern island of Mindanao for another year, which the president said was needed to fight armed groups there.

Mindanao was placed under martial law in May, after local militants backed by the Islamic State seized the city of Marawi. After months of fighting, the government declared victory there in October. But Mr. Duterte said Friday that a yearlong extension of martial law was needed to ensure the “total eradication” of militancy in Mindanao, an impoverished region where various armed groups have been active for decades.

Both houses of Congress approved Mr. Duterte’s request overwhelmingly, despite opposition lawmakers’ warnings that martial law was no longer needed and that to extend it risked eroding constitutional values. The martial law edict gives the military widespread powers, including the ability to carry out warrantless arrests and set up roadblocks and checkpoints.

The president’s request for an extension came shortly after he halted efforts to reach a peace deal with the underground Communist Party of the Philippines, whose armed unit, the New People’s Army, has stepped up attacks in remote communities on Mindanao and elsewhere.