Kurdish rebels have halted their pullout from Turkey, accusing Ankara of breaking its part of a ceasefire deal, but vowed to respect a truce, 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 estimated 2,500 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 the peace process could not 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 it 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 government of failing to pass a package of democratic reforms designed to reinforce the rights of Turkey's Kurdish minority, believed to number up to 15 million.

In return for withdrawing its 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 degree 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 ruled out a general amnesty for the rebels, including for Ocalan, and the right to education in Kurdish.

Erdogan also questioned the extent of the PKK pullout, estimating that barely 20 percent had left Turkey for bases in Iraqi Kurdistan and that most were children or elderly.

Ocalan has been in negotiations since late 2012 with Turkish authorities for an end to the Kurdish conflict, which has cost more than 40,000 lives since 1984.

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

The PKK's recently appointed leader Cemil Bayik, considered a hardliner by Ankara, has repeatedly accused the government of attempting to sabotage the fledgling peace process.

Selahattin Demirtas, a co-chairman of the Kurdish Peace and Democracy Party (BDP), also warned late last month that Erdogan was wasting precious time in implementing his part of the deal.

And another BDP deputy leader, Gultan Kisanak, hailed the PKK for its commitment to respect the ceasefire.

"We have warned the government several times" about possible delaying tactics, she told the press. "We hope that it will start to accept its responsibility."

Talks on the constitutional reform needed to introduce some of the changes demanded by the Kurds are stalled by wrangling between the AKP and its political rivals.

A significant portion of Turkish public opinion remains opposed to any negotiations with Ocalan and his rebel group.

Speaking to reporters on his way back from Buenos Aires on Sunday, Erdogan remained upbeat however about the peace process.

"I don't think there will be any major obstacle... What matters is that the (Kurdish) people want this process to continue," he said.

But he has made clear that a general amnesty for the rebels including Ocalan and the right to Kurdish-language education are "not on the agenda".

"We must continue our work and fight to make terror stop," Deputy Prime Minister Bekir Bozdag told the press on Monday.