A group of security personnel for Philippine President Rodrigo Duterte was ambushed early Wednesday by Communist rebels along a highway on the southern island of Mindanao, leaving a civilian militiaman dead and five security officers wounded.

A local correspondent for The Manila Times reported the attack took place in Arakan, Cotabato Province; a remote mountainous area considered a hotspot for activity by the New People’s Army (NPA), the armed wing of the Communist Party of the Philippines (CPP).

Rebels disguised as government troops

The security detail, traveling in two vehicles, was waylaid at a checkpoint along the highway manned by NPA fighters wearing military uniforms, The Manila Times report said.

A civilian militiaman was shot dead when he identified himself, the report added, setting off an hour-long gun battle between the Presidential Security Group (PSG) detail and as many as 150 rebels.

The PSG group was traveling from the southern Mindanao city of Davao, the hometown of President Duterte, to the city of Cagayan de Oro on Mindanao’s northern coast. The commander of the Philippine Army’s 39th Infantry Battalion, which is based in the area, said five wounded guards were taken to Davao for medical treatment.

Rising tensions

The attack comes as the Philippine legislature is preparing to debate extending martial law in Mindanao, which Duterte imposed on May 23 after Islamic State-backed terrorists attacked the city of Marawi.

On May 25, the CPP leadership based in the Netherlands ordered the NPA to increase its attacks against the Philippine military in response to the martial law declaration, according to a report by CNN Philippines. The move by the rebels prompted Duterte to cancel what would have been a fifth round of peace talks between the government and the CPP.

The government’s lead negotiator said in a statement that the government “would not proceed” with talks until a “more conducive environment” was established.

The Communist insurgency in the Philippines, which has gone on for 48 years, is the second-longest such rebellion in Asia. Although it is most active in Mindanao, the NPA carries out hit-and-run attacks throughout the country.

Most recently, it raided two towns in the central province of Iloilo, taking advantage of the military’s preoccupation with the battle for Marawi farther south.

The left-leaning Duterte had made finalizing a peace agreement with the CPP one of his campaign promises before being elected last year, but since then has publicly expressed frustration with the Communists’ unwillingness to observe a ceasefire.