MANILA, Philippines — The Philippine president has formally declared that communist guerrillas waging a decades-long rebellion are terrorists, in his latest move jeopardizing the resumption of peace talks with the insurgents.

President Rodrigo Duterte’s spokesman, Harry Roque, told reporters Tuesday that the Philippine leader signed a proclamation that the Communist Party of the Philippines and its armed wing, the New People’s Army, are a terrorist organization, in the first step of a legal process to officially ban them.

If approved by a court, the communist guerrillas will be the second group to be proscribed under a seldom-used 2007 anti-terror law after the Abu Sayyaf, a brutal Muslim extremist group that was blacklisted in 2015 for involvement in ransom kidnappings, beheadings and bombings.

It took about five years for state prosecutors to secure court approval for the Abu Sayyaf’s proscription, which was aimed at making membership in the group a crime and allowing government forces to crush the militants faster.

Duterte, who calls himself the country’s first leftist president, revived peace talks with the Maoist rebels and gave them political concessions, including the appointment of left-wing activists to Cabinet posts, when he became president last year. But the talks, which have been brokered by Norway, soon crumbled after the volatile leader protested continued rebel attacks on troops.

He has walked back from a previous hard-line stance against the guerrillas and allowed the resumption of the talks, but his latest moves deal a serious blow to prospects for a return to the negotiating table and could provoke rebel attacks.

Security officials welcomed Duterte’s move. “We have long since maintained that the Communist Party of the Philippines-New People’s Army is a blight to the Filipino people, with its members engaging in constant criminal activities and wanton acts of terror,” Defense Secretary Delfin Lorenzana said.

“The government has walked the extra mile to accommodate them by resuming the talks,” Lorenzana said, accusing the guerrillas of imposing unreasonable conditions in the talks and continuing criminal acts like kidnappings, attacks on government forces and extortion.

The guerrillas have scuttled peace talks in the past after accusing the government of helping the United Nations and the United States designate them as terrorists. The rebellion they have waged mostly in the countryside has left more than 40,000 combatants and civilians dead and hampered development in some of the country’s poorest regions.