Three military police officers were killed in an ambush early Saturday in a restive region of southern Chile, authorities said, in the worst such violence in years.

"This morning we received the grave and painful news of an attack in Arauco province in which three Carabineros were killed," President Gabriel Boric announced on the social media platform X.

He traveled to the area with a large contingent, including top military and congressional officials and the president of the Supreme Court, and later declared three days of national mourning.

In Santiago, hundreds of people gathered outside the presidential palace to protest the killings.

The bodies of the three officers were found in a burned-out armored patrol vehicle on a road near the city of Concepcion, some 500 kilometers (300 miles) south of capital Santiago. They appeared to have been shot.

The area had been militarized after a series of arsons, mostly attributed to radical groups of Mapuche, Chile's largest Indigenous group, which has demanded the restitution of ancestral lands.

The attack occurred as Chile's Carabineros, or military police, were celebrating the 97th anniversary of their founding.

"This was not coincidental, it was not random," said Ricardo Yanez, director general of the Carabineros.

The attack came the same week that Hector Llaitul, a leader of CAM, one of the groups that has claimed the arson attacks, was convicted of "attacks against authority" and related crimes. He faces up to 25 years in prison.

Boric denounced those behind the latest attack as "terrorists" and told fellow Chileans, "we will find the whereabouts of the perpetrators of this terrible crime."

Earlier this week Boric's administration had announced that violent incidents in Arauco had been cut in half since he took office in March 2022.