Turkey's Kurdish rebels have halted withdrawing their fighters from Turkish territory, which is a key part of a peace plan, accusing Ankara of not abiding by the deal's terms, a pro-Kurdish news agency reported on Monday.

Under a roadmap to end the three-decade old insurgency, the Kurdistan Workers Party (PKK) began in May withdrawing its fighters from Turkey to safe havens in Iraq's autonomous Kurdistan region.

No deadline was set for the withdrawal, but a ceasefire agreement reached in March said that the peace process cannot proceed further until it is completed.

In a statement cited by Firat News, the PKK armed movement said "the Turkish government's attitude of not progressing on the Kurdish question was behind this situation," but vowed to respect the ceasefire with Turkish forces.

"The withdrawal of fighters has been stopped," said the statement from the PKK, which is listed as a terrorist organisation by both Ankara and its Western allies.

"The truce will be maintained... to allow the Justice and Development Party (AKP) government to begin initiatives supporting the (peace) plan" of Abdullah Ocalan, the imprisoned PKK leader, it said.

In the statement, the PKK accused the Islamic-rooted government of failing to adopt in parliament a package of democratic reforms designed to reinforce the rights of the Kurdish minority in Turkey, who number an estimated 15 million.

In return for withdrawing its estimated 2,500 fighters in Turkey, the PKK is demanding amendments to the penal code and electoral laws as well as the right to education in the Kurdish language and a form of regional autonomy.

Turkish Prime Minister Recep Tayyip Erdogan said last month that his government was still attached to the principle of peace with the PKK. But he said that a general amnesty for the rebels, including for Ocalan, and the right to education in Kurdish, was not in the offing.

Erdogan also questioned the extent of the PKK pullout, estimating that barely 20 percent of them had left Turkey for bases in Iraqi Kurdistan.

The jailed leader Ocalan has been in negotiations since late 2012 with Turkish authorities for an end to the Kurdish conflict, which has cost some 45,000 lives since 1984.

Ocalan, serving a life sentence for treason and separatism on Imrali island off Istanbul since 1999, announced a historic ceasefire with the government in March.