Russia, Turkey and Iran have agreed to set up de-escalation zones in Syria for six months, negotiators for the three countries have said in a joint statement during the sixth round of talks in the Kazakh capital, Astana.

The zones will include, fully or partly, Eastern Ghouta and the provinces of Idlib, Homs, Latakia, Aleppo and Hama, according to a statement issued on Friday.

The six-month term may be extended in the future.

The plan calls for the cessation of hostilities between anti-government groups and forces fighting on behalf of Bashar al-Assad in four so-called de-escalation zones in mainly opposition-held areas of the country, with Russia, Turkey and Iran to act as guarantors.

READ MORE: Syria's 'de-escalation zones' explained

The statement said representatives from the three countries were still discussing what forces to deploy in Idlib, which is under the control of an alliance spearheaded by the former al-Qaeda offshoot, al-Nusra Front.

"Delegations from Turkey, Russia and Iran determined the borders of a fourth de-escalation zone that will be established in Idlib province in talks yesterday and today," Anadolu news agency said, citing sources attending the meetings in Astana.

The UN's special envoy to Syria, Staffan de Mistura, said the creation of a fourth de-escalation zone is a positive development.

"We really welcome this agreement today because we have always been pushing for de-escalation," he said.

"This is what the people of Syria haven been asking and the fact of adding new areas to this de-escalation is crucial," Mistura added. "It already has reduced fighting in many areas."

Turkey's pro-government Yeni Safak newspaper said in an unsourced report on Friday that the three countries planned to divide the Idlib region in three, with Turkish forces and opposition fighters in the northwest region bordering Turkey.

It said Iranian and Syrian army forces would be deployed to the southeast, with Russian forces in between those two zones.

Though the plan for de-escalation zones was signed by Syrian-government backers Iran and Russia in May, diplomats failed to hammer out the details over boundaries and policing during the last round of Astana talks in July.

The deal laid out the areas where fighters and government forces should halt hostilities, including air raids, for six months. More than 2.5 million people are believed to live in the zones.

This is the first plan to envisage armed foreign monitors on the ground in Syria.

Troops from the three countries are expected to help to secure the safe zones.

Al Jazeera's Charles Stratford, reporting from Astana, said that the agreement is a "sign of progress", but questions loom over its implementation.

"There are concerns by the opposition with respect to having Iranian forces on the ground as monitors in the designated areas," he said. "The opposition is staunchly against any real presence by Iran in Syria."

'Unhindered' humanitarian aid

Russia will continue to fly over the areas but refrain from conducting air raids.

The Syrian government is to allow "unhindered" humanitarian aid into opposition-held areas, and public services such as electricity and water are to be restored where they have been cut off.

Syria's conflict evolved from a government crackdown on protests in 2011 to become a devastating war that has drawn in world powers, including Russia and a US-led international coalition.

Russia has pushed the talks in Astana since the start of the year as it seeks to pacify Syria after its game-changing military intervention in 2015 on the side of Assad.

The next round of talks in Astana are scheduled for October