Western governments are growing impatient with Syria's failure to follow up promptly on a first small shipment of chemical weapons and fear Damascus will miss a deadline to hand over all toxins by mid-2014.

Sources at the Organisation for the Prohibition of Chemical Weapons (OPCW), which is jointly overseeing the destruction process with the United Nations, said the concerns have been raised during internal discussions, but have not yet been reported to the U.N. Security Council.

Syria agreed to dismantle its entire chemical weapons program by June 30, under a deal proposed by Russia and agreed with the United States. It has until March 31 to relinquish around 500 tonnes of the worst substances, including more than 20 tonnes of mustard gas stored in liquid form.

That deadline had already been expected to slip, but the concern now is that the entire destruction program will be pushed back. Syria says the program faces security concerns.

Failure to eliminate its chemical weapons could expose Syria to consequences that might include sanctions, although these would have to supported in the U.N. Security Council by Russia and China, which have so far refused to back such measures against President Bashar al-Assad.

The decision to do a deal with Damascus to eliminate its chemical arsenal removed the likelihood that the United States and its allies would bomb government positions in Syria to punish it for a chemical attack last August and underlined the limits to international action against Assad.

More recently, the international response to allegations of atrocities by Assad's security apparatus - the systematic torture and killing of thousands in government jails - has so far been muted. Internationally sponsored peace talks in Geneva have got off to a difficult start and are not expected to produce a settlement to the war.

It has been more than two weeks since the first shipment of chemicals reached the northern port of Latakia on January 7 and was transferred onto a Danish vessel.

But the first batch of 16 metric tonnes (17.63 tons) was only just over one percent of the 1,300 tonnes of chemical weapons declared by Syria to the OPCW and was possibly already in or near the port and did not have to be transported far.

Several foreign governments funding and assisting the process had expected more shipments would have already been made, the sources said, and frustration is growing.

"It's starting to become a problem and they are at risk of being reported (to the United Nations) for non-compliance," one source involved in the discussions told Reuters on condition of anonymity.

While there is widespread frustration at the slow pace of the chemical weapons handover, "no one is seriously considering reporting this to the Security Council," another high-level source involved in the discussions said.

"There is frustration. There is no doubt about that," the source said. "But the issue of non-compliance will occur when people believe they are being misguided and that there is a scheme to stall. We're not there yet."

Eliminating Syria's chemical weapons program under such tight deadlines amid a civil war was overly ambitious from the beginning, experts had warned.

Syria's toxic stockpile is spread over storage sites across the country and the chemicals must be transported by road through territory where Syrian forces have recently battled rebel forces.

The plan also faces huge logistical challenges, requiring cooperation between a long list of countries, including Russia, Denmark, China, Britain, Germany, Italy and the United States.

Security is another major concern. Syria's representative to the OPCW said two storage sites were attacked by assailants and that serious threats had been made against the operation, causing a delaying in shipments.

The OPCW's director, Ahmet Uzumcu, said on January 16 that interim deadlines might slide due to security and other problems, but that he was "confident" that all the chemicals could be destroyed by the end of June.

Other sources said if Syria does not start shipping out chemicals in large quantities in coming weeks, it is likely the June 30 deadline to dismantle the entire chemical weapons program will be missed.

"We had been giving them the benefit of the doubt because cooperation began smoothly, but now it looks like they are making excuses," another source who attended discussions said.

"We need to see some more shipments, and not of the same size as this first small one," the source said.

The high-level OPCW source said Syria does not plan to ship more chemicals until transport containers have been fitted with armor and other security equipment, such as radio scramblers.

"The Syrians don't feel comfortable shipping the containers unless all the security equipment is in place," the source said.

Western government have said they will not provide equipment which could be used to support Assad's forces and it is unclear what Russia, Syria's main international backer, will do.

Syria's agreement to give up its chemical weapons followed an August 21 sarin gas attack that Western nations blamed on Assad. Damascus blames rebels for the attack, which killed hundreds of civilians in the outskirts of the capital.

The OPCW is about to complete a tender process to select commercial destruction facilities to take the bulk precursor chemicals. It is set to announce its decision in early February, but Germany and Britain have agreed to take a portion.

The most toxic substances, around 500 tonnes, will be destroyed on the Port Ray, a five-storey U.S. cargo vessel fitted with a so-called hydrolysis system, which will break down the chemicals at sea.

The unprecedented decision to ship chemical weapons overseas was promoted by heavy fighting in Syria's civil war, which has killed more than 100,000 people and forced millions to flee.-Reuters