Philippine President Rodrigo Duterte gestures while delivering a speech during the 115th Police Service Anniversary at the Philippine National Police (PNP) headquarters in Quezon city, metro Manila, Philippines August 17, 2016. [Photo/VCG]

MANILA - Philippine President Rodrigo Duterte declared on Saturday an indefinite ceasefire to pave the way for resumption of peace talks with communist rebels next week, said Presidential Peace Adviser Jesus Dureza.

The peace talks are scheduled for Aug 22 in Oslo, Norway.

President Duterte has "restored the effects of the unilateral ceasefire with the Communist Party of the Philippines and the National Democratic Front effective 12 midnight tonight, Aug 21," Dureza told a news conference at the international airport before leaving for Oslo with the government panel.

"The duration of the ceasefire will last for as long as necessary to bring peace in the land," he said.

Duterte declared a unilateral ceasefire on July 25 but scrapped it six days later after the rebels failed to reciprocate and attacked and killed a militia man.

"The enabling environment brought about by this 'silencing of the guns' will hopefully go a long way in bringing about an expeditious and early resolution to our differences and aspirations that have long divided us as a people," said Dureza.

He said the restoration of the ceasefire came a few days after Duterte has released from detention about 20 prisoners who are needed in the peace negotiations.

"As we speak there is continuing efforts to make available in Oslo peace talks resumption as many of them as possible," Dureza said, referring to the remaining political prisoners that will take part in the talks as "consultants."

The Philippine government released from jail on Friday two communist leaders, Benito Tiamzon and his wife, Wilma, to allow them to participate in the Oslo talks.

The Tiamzons are the highest-ranking communist leader in detention after they were arrested in 2014. The government said Benito Tiamzon was the chairman of the Communist Party of the Philippines while his wife Wilma was the secretary general.

A few hours after their release, the Communist Party of the Philippines declared a seven-day unilateral ceasefire that will take effect 12:01 am on Aug 21 and will last until 11:59 pm on Aug 27.

"This ceasefire declaration is encouraged by the (Philippine government's) facilitation of the release of the nearly all National Democratic Front of the Philippines consultants who are set to participate in peace negotiations in the course of the next several months," the rebels said in a statement.

The Oslo talks are expected to tackle "social and economic reforms, political and constitutional reforms, end of hostilities and disposition of forces, ceasefire, joint security and immunity and release of political detainees," according to Dureza.

The Duterte administration is trying to forge peace with the communist rebels. Talks between the government and the rebels began in 1986, but failed to lead to a resolution over the years.

The communist rebellion began in 1969 and reached its peak in 1987 when it boasted 26,000 armed guerillas. However, the movement has since dwindled due to differences in strategy and tactics and the arrests of many of its top leaders in the late 1980s.

The military estimates the current number of communist armed rebels to be around 4,000.