NTB scanpix via AP, Berit Roald
Norwegian Foreign Minister Boerge Brende, third right, and Elisabeth Slaattum, third left, from Norwegian Foreign Minister's office, pose with Philippine Presidential Advisor on the Peace Process Silvestre Bello III, left, National Democratic Front of the Philippines (NDFP) chief political consultant and Communist Party of the Philippines founder chair Jose Maria Sison, second left, and Philippine Presidential Peace Talks Adviser Jesus Dureza, second right, during their meeting in Oslo, Norway, Monday, Aug. 22, 2016. Norway is hosting a four-day peace talks between the Philippine government and the NDFP that will focus on resolving the root problems of an insurgency that has left more than 150,000 combatants and civilians dead and undermined the Philippines' economic development.

OSLO, Norway — Peace talks between the government of Philippine President Rodrigo Duterte and communist rebels aimed at ending one of Asia's longest-running rebellions formally resumed Monday, with hosts Norway cautioning against a quick result.

Some 150,000 people have died in the conflict that began almost half a century ago.

"We are going to have five very demanding days here ... but I would like to congratulate the two parties on the resumption of the formal peace talks," said Norwegian Foreign Minister Borge Brende.

The negotiations were facilitated by a cease-fire imposed by Duterte and a truce announced by the rebels that began Sunday.

The peace process, which has dragged on for decades, broke down in 2001 when the Maoist rebels backed out after the U.S. government — followed by the European Union — placed them on a list of terrorist organizations. It was resumed in 2011 under the leadership of Norway.

Although less numerous and less violent than Muslim separatist rebels in the country's south, the Maoists have fought and outlived successive Philippine administrations for nearly 50 years, holding out against constant military and police offensives. They draw support from those dissatisfied with economic inequality, especially in the countryside, and the Philippines' alliance with the U.S.

The rebels trace their roots to a communist party whose guerrilla wing helped fight Japanese occupation forces in World War II and their ranks swelled after dictator Ferdinand Marcos declared martial law in 1972. They set up jungle camps over the sprawling archipelago as launching pads for raids targeting the military and police, large agricultural and mining estates as well as U.S. forces, which maintained major bases in the Philippines until 1991.

As they sat down to talk in the Norwegian capital, both sides agreed that an important factor has changed: a Philippines president strongly supporting the peace process with cease-fires, the release of political prisoners, and the appointment of two allies of the guerrillas to Cabinet posts in concessions that fostered the resumption of talks.

"The NDFP (National Democratic Front of the Philippines) are optimistic that objective conditions and subjective factors in the Philippines are more favorable than ever," said Jose Maria Sison, founder of the Communist Party of the Philippines. "He offers more hope for the advance and success of the peace negotiations than previous presidents and regimes."

Attending the talks are two top Philippine communist rebel leaders who were released from a maximum-security jail on Friday.

One of them, Benito Tiamzon, said he had a lot of catching up to do. "We have to cram," he said.

Participants in Oslo told the AP that the talks were expected to last until Friday when an agreement could be signed outlining a roadmap to continue the peace process.