The New People's Army (NPA) kidnapped three army troops who were found dead hours later at a mountainous area on the southern island of Mindanao Wednesday, regional military spokesman Major Ezra Balagtey told AFP.

The NPA also ambushed another military unit elsewhere on the island, killing a junior officer, while three other soldiers were later kidnapped in another area of Mindanao early Thursday, Balagtey added.

"We are expecting they will be on (the) offensive again. It's not the positive development that we want to happen," Balagtey said.

However the government and the rebels have said peace talks, which are set to resume in Norway in April, would go ahead.

On Wednesday the 4,000-member NPA's parent organisation the Communist Party of the Philippines announced it was ending a five-month-old unilateral ceasefire and accused President Rodrigo Duterte's government of treachery and human rights abuses.

The rebels also criticised Duterte's failure to grant amnesty and freedom to nearly 400 jailed guerrillas, after the president released 18 jailed rebel leaders at the start of the talks last year.

The communists have been waging an insurgency since 1968 that the military says has claimed 30,000 lives, to overthrow a capitalist system that has created one of Asia's biggest rich-poor divides.

Duterte, a self-styled socialist who was swept to power in elections last year, restarted peace talks that had been on and off for 30 years.

The two sides separately declared ceasefires in August, and the informal arrangement largely held as they continued discussions in Rome last week.

But the rebels rejected government overtures to sign a formal ceasefire and peace settlement this year, warning such a pact was unlikely to be achieved before 2019.

Duterte on Thursday criticised the rebels for rejecting his government's formal ceasefire offer and for insisting that he free hundreds of jailed guerrillas.

While the military establishment has publicly endorsed the peace talks, Duterte suggested the support was qualified.

"Don't push me against the wall because the military might not like it, and if the military ousts me or kills me you'll have nobody to talk to," he said in a speech in his southern hometown of Davao.

Duterte said he needed military and police backing for the talks to succeed, adding general amnesty and freedom for all jailed rebels will only come after a peace settlement.

"Nurture respect in everybody's heart because if respect is gone they will topple you," he said, citing a lesson he said he learnt from his late father.