ASTANA - Key international players in Syria's civil war gathered in Kazakhstan Wednesday for a fresh round of talks aimed at pushing a Russian-led plan to ease fighting on the ground.

Representatives from regime backers Russia, Iran and rebel supporter Turkey held "talks on an expert level" to lay the groundwork ahead of the start of two days of meetings that will include the Syrian regime and opposition representatives, Kazakhstan's foreign ministry said.

The talks in Astana are the sixth round of negotiations Moscow has spearheaded since the start of the year as it seeks to pacify Syria after its game-changing intervention on the side of leader Bashar al-Assad. This time around the sides are looking to nail down details of a proposed "de-escalation" zone in the northern Idlib province, after Moscow ploughed on with setting up three other safe areas around the country in a move that has seen violence drop.

There remain major disagreements over which force will be sent to police the zone covering rebel-held Idlib - on Syria's northern border with Turkey - as Ankara and Tehran jockey for influence.

Russia has so far deployed military police to patrol the boundaries of three zones agreed in the south, in Eastern Ghouta near Damascus, and in part of the central Homs province.

Yehya al-Aridi, an advisor to the Syrian opposition, confirmed the rebel delegation would arrive in Astana on Wednesday evening, headed by Ahmed Berri, chief of staff of the Free Syrian Army.

"The aim of our participation in this round is to strengthen the de-escalation zones in Syria, in Eastern Ghouta, the south, and north of Homs, and to discuss many violations that took place since the ceasefire agreement was signed in Ankara at the end of the last year," al-Aridi told AFP.

A Syrian pro-regime newspaper Al-Watan reported that the government's delegation, led by the country's United Nations envoy Bashar al-Jaafari, had arrived in Astana early on Wednesday.

The de-escalation zone in the south of Syria has also proved sensitive as it lies close to the borders of US-allies Israel and Jordan, and Washington is keen to make sure that Iran and its proxy forces are kept out.

The State Department confirmed that Acting Assistant Secretary of State David Satterfield will travel to Astana Thursday as an observer.

"Iran's activities in Syria and unquestioning support for the Assad regime have perpetuated the conflict and increased the suffering of ordinary Syrians," the State Department said in a statement.

Syria army tries to encircle

IS in Deir Ezzor

After breaking an Islamic State group blockade, Syria's army is seeking to encircle the remaining militant-held parts of Deir Ezzor city, a military source said Wednesday.

The city is the capital of oil-rich eastern Deir Ezzor province, regarded as a strategic prize by both Russian-backed Syrian troops and US-backed fighters. Last week, Syria's army and allied fighters broke a years-long IS siege of Deir Ezzor, entering two regime-held sections of the city that had been cut off from each other.

Since then, the army has brought reinforcements to the city and is seeking to oust IS from eastern neighbourhoods that run along the Euphrates river, which slices diagonally through the province.

"The army is seeking to encircle Daesh from three sides by controlling the parts of the western bank of the Euphrates river," the source told AFP, using the Arabic acronym for IS.

Troops would target riverside territory on the city's northwestern edges as well as strategic areas on its southern outskirts, including the key military airport and the village of Al-Jafra, on the banks of the Euphrates.

The operation seeks to "oust Daesh from the city and the province completely," the military source said.

Rami Abdel Rahman, head of the Syrian Observatory for Human Rights monitor, also reported that "fierce fighting has been ongoing since yesterday as the army seeks to expel the militants and reach the western bank of the Euphrates."

If the army captures Al-Jafra, "Deir Ezzor will be encircled from three sides, so Daesh will have no way out except the Euphrates which is within firing range of regime artillery and Russian warplanes," he added.

As the Syrian army backed by Russian air support battles IS in Deir Ezzor, a separate offensive by the US-backed Syrian Democratic Forces is under way on the eastern side of the province.

The operation by the alliance of Kurdish and Arab fighters began over the weekend, but the SDF has said it was not coordinating the fight with the regime.

Air strikes by Russian and US-led coalition war planes in support of the separate offensives have killed dozens of civilians in recent days.

On Wednesday, the Observatory said suspected US-led coalition strikes on several parts of eastern Deir Ezzor province overnight and throughout the day killed 12 people.

On Tuesday, the monitor reported 35 people killed in Russian and US-led strikes on either side of the Euphrates.

More than 330,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.