Syria has given up less than 5 percent of its chemical weapons arsenal and will miss next week's deadline to send all toxic agents abroad for destruction, sources familiar with the matter said on Wednesday.

The deliveries, in two shipments this month to the northern Syrian port of Latakia, totalled 4.1 percent of the roughly 1,300 tonnes of toxic agents reported by Damascus to the Organisation for the Prohibition of Chemical Weapons (OPCW), said the sources, who spoke on condition of anonymity.

"It's not enough and there is no sign of more," one source briefed on the situation said.

The internationally backed operation, overseen by a joint OPCW-United Nations mission, is now 6-8 weeks behind schedule. Damascus needs to show it is still serious about relinquishing its chemical weapons, the sources told Reuters.

The issue is to be discussed at a meeting of the OPCW's executive council on Thursday in The Hague, a senior U.S. State Department official told Reuters.

The meeting will focus on the lack of progress and confirm that no more than 5 percent of the chemical weapons material has been removed from Syria, the official said, speaking on condition of anonymity.

Failure to eliminate its chemical weapons could expose Syria to sanctions, although these would have to be supported in the UN Security Council by Russia and China, which have so far refused to back such measures against Syrian President Bashar Assad.

The deal under which Syria undertook to eliminate its chemical arsenal stopped the United States and its allies from launching bombing raids to punish Assad for a chemical attack last August and made clear the limits to international action against him.

UN Secretary-General Ban Ki-moon suggested in a report to the Security Council this week that shipments had been unnecessarily delayed and urged the Syrian government to speed up the process.

U.S. Secretary of State John Kerry urged his Russian counterpart Sergei Lavrov during a phone call on Wednesday to "press the (Syrian) regime to move forward with the necessary steps on the chemical weapons process," State Department spokeswoman Jen Psaki told a briefing.

Message to Syria

A senior Western diplomat, speaking on condition of anonymity, said that the UN Security Council will be briefed on the issue by mission head Sigrid Kaag next week.

"All the indications are, and the secretary-general's report makes clear, that actually the regime has been sort of stalling on the implementation of the agreement," the diplomat said.

"It will be important what Sigrid Kaag says about whether she thinks these delays are deliberately politically motivated and why or whether there's any truth in the weather, the security and those more technical aspects," he said.

Another senior Western diplomat said the Syrian government is "teasing us" by dragging its heels but doing enough to avoid being declared in non-compliance with its obligation to destroy its chemical weapons program.

The second diplomat added that Russia would never permit the UN Security Council to declare Assad's government in non-compliance with its duty to eliminate its poison gas program.

"The Russians will never accept it," the second diplomat said, adding that Western powers were also reluctant to do anything that could be seen as undermining the Geneva peace talks between Assad's government and the opposition.

"Our impression is that they (Assad's government) are managing this issue in parallel with the Geneva discussion," he said. "Everything is blocked so they are blocking on the chemical weapons to remind us" of their power on this issue.

Syria, where civil war has killed well over 100,000 people and forced millions to flee, has blamed delays on security obstacles. It said the mission could not be safely carried out unless it received armored vehicles and communications equipment.

A source briefed on the situation said: "Yes, it's true there is a war, but have you ever heard of a civil war without security issues? They have all the necessary means they need for transportation. Now they need to start shipping the chemicals out."

Under a deal agreed by Russia and the United States after the August 21 sarin gas attack, Syria vowed to give up its entire stockpile by mid-2014. The rocket attacks in the outskirts of Damascus killed hundreds, including women and children.

Eradicating Syria's chemical weapons stockpile, including sarin, mustard gas and VX, requires massive foreign funding and logistical support.

The bulk of the most toxic substances are to be destroyed on the Cape Ray, a U.S. cargo ship now en route to the Mediterranean that will be loaded with the chemicals at an Italian port. The remainder will go to several commercial waste processing facilities, including in Britain and Germany.