Ahead of fresh peace talks starting in Italy on Thursday, the National Democratic Front of the Philippines also warned that forces on the ground were urging an end to a ceasefire as they became frustrated with the government's "broken promises".
"The NDFP goes into the third round of formal talks in Rome determined as always to persevere with the peace talks but increasingly troubled by the other party's sincerity," the communists' chief negotiator, Fidel Agcaoili, said in a statement.
At least 30,000 people have died in the conflict, according to the military.
President Rodrigo Duterte, who describes himself as a socialist, has made ending the rebellion one of his top priorities.
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He launched the peace process soon after he took office in June last year and installed three communists in his cabinet.
Both sides agreed to a temporary ceasefire during the first round of talks in Norway last August.
The government said then it was aiming for a final peace deal within 12 months.
Those economic and political reforms have yet to be agreed, and are meant to be discussed in Rome.
Meanwhile, familiar grievances that derailed peace efforts under previous Philippine presidents appear to have returned to haunt the current negotiations.
The communists have long demanded that hundreds of jailed communists be released before they will consider making major concessions in peace talks.
Duterte released 18 top leaders to kickstart the peace process but the communists are demanding another 434 rebels be freed immediately.
"My aces are in prison," he said, referring to the jailed communists.
"If I released them all my cards would lost. There would be nothing else to talk about.