Danish support vessel L17 "Esbern Snare" of the Danish-Norwegian task group which will transport Syria's chemical agents for destruction performs training in the Mediterranean Sea, in this handout photo released to Reuters on Jan 5, 2014 by the Norwegian Armed Forces. [Photo/Agencies]

BEIRUT - Syria has started moving chemical weapons materials out of the country in a crucial phase of an internationally backed disarmament programme that has been delayed by war and technical problems.

The Organisation for the Prohibition of Chemical Weapons said on Tuesday that "priority chemical materials" were transported to the port of Latakia and onto a Danish vessel which was now sailing towards international waters.

Syria agreed to abandon its chemical weapons by June under a deal proposed by Russia and agreed with the United States after an August 21 sarin gas attack that Western nations blamed on President Bashar al-Assad's forces. Damascus blames rebels for the attack.

War, bad weather, bureaucracy and technical issues meant a December 31 deadline for the removal of the most deadly toxins from Syria was missed.

The OPCW did not disclose what percentage of Syria's toxic arsenal -- which totals 1,300 tonnes in all -- had been removed but said nine containers of the most dangerous chemical materials were on the Danish cargo vessel.

"The vessel has been accompanied by naval escorts provided by Denmark and Norway, as well as the Syrian Arab Republic," a statement said. "It will remain at sea awaiting the arrival of additional priority chemical materials at the port."

Maritime security was being provided by Chinese, Danish, Norwegian and Russian ships.

Government forces have taken back control of the highway linking Damascus to the coast which is needed to transport the toxins. Rebel were ousted from three towns along the road but activists say convoys moving along it will remain vulnerable to rebel ambushes.

Washington welcomed the removal of chemical materials and said Assad's government appeared to be sticking to the deal.

"Much more needs to be done," State Department spokeswoman Jen Psaki told a news briefing, adding: "We have no reason to believe that the regime has gone back on any aspect of their promise."

REBEL INFIGHTING

On the battlefield, Syria's bloodiest bout of rebel infighting since the war started nearly three years ago prompted the head of an al Qaeda-linked rebel group to called for a ceasefire between opposition factions.

An audio recording from the leader of the powerful Nusra Front, known as Abu Mohammed al-Golani, laid much of the blame for the fighting on an al Qaeda splinter group known as the Islamic State in Iraq and the Levant (ISIL).

While both groups have roots in the global Islamist network and welcome foreign militants, the Nusra Front has cooperated more with other rebel groups and has largely avoided the power struggles that ISIL has faced since wresting control of many opposition-held areas from other groups.

"Many rebel units have committed transgressions, just as the mistaken policies followed by played a prominent role in fuelling the conflict," Golani said.

ISIL has also been fighting in Iraq, where it faces an onslaught by army tanks and artillery around the city of Falluja, whose local leaders have urged the Qaeda-linked militants to leave before being attacked.

ISIL gunmen want to reconquer Iraq's Anbar province in pursuit of their goal of creating a radical Islamic state out of the chaos of neighbouring Syria's civil war.

More than 274 people have been killed in the rebel-on-rebel clashes in Syria since they began on Friday, according to the Syrian Observatory for Human Rights, an opposition monitoring group.