(Adds details on chlorine attack investigation)
By Anthony Deutsch
AMSTERDAM May 22 (Reuters) - Syria has made no progress in relinquishing a last batch of chemical weapons it says is inaccessible due to fighting, making it increasingly likely it will miss a final deadline to destroy its toxic stockpile, Britain said on Thursday.
The British deputy representative to the Organisation for the Prohibition of Chemical Weapons (OPCW) told delegates in The Hague that packaging material had arrived for the 100 metric tonnes of toxic chemicals.
"But there is still no sign of any movement of chemicals, nor any indications of a time scale for a move," said the statement, a copy of which was obtained by Reuters.
Syrian President Bashar al-Assad, embroiled in civil war with rebels fighting to oust him, agreed last year to hand over the country's entire chemical weapons stockpile after hundreds of people were killed in a sarin gas attack near Damascus.
The agreement with Russia and the United States averted Western military strikes threatened in response to the worst chemical weapons atrocity in decades, which has been blamed by Washington on Assad's government.
His government, which denies the allegation and blames the rebels, still has roughly 7 percent of 1,300 tonnes it declared to the OPCW, enough highly toxic material to carry out a large-scale attack.
It has missed several deadlines, most recently its own promise to hand over the remaining chemicals by April 27. It has also failed to destroy a dozen facilities that were part of the chemical weapons programme.
Under the deal, Syria's entire stockpile is supposed to have been destroyed by mid 2014, but "it is growing ever clearer that the 30 June deadline will not be met", the British statement said.
OPCW head Ahmet Uzumcu said later the organisation, which won the Nobel Peace prize last year, was preparing for on-site investigations in Syria into allegations of chlorine gas attacks in recent months.
The Chemical Weapons Convention, which Syria joined in October as part of the U.S.-Russian agreement, does not ban chlorine, but does ban its use as a weapon. Damascus denies allegations of military use of the chemical, which has been reportedly dropped from helicopters in "barrel bombs".
France has alleged that Syria has concealed chemical weapons and also may have carried out attacks with chlorine 14 times in recent months.
Uzumcu said the Syrian authorities had agreed to provide security for inspections of sites within government controlled areas, but that it would be a "particularly challenging undertaking" gaining access to territory outside its control.
OPCW inspectors investigating earlier allegations of chemical weapon use in Syria were fired at by snipers, and shells and rockets landed near their hotels.
"The alleged use of chlorine in Syria is of grave concern to the OPCW and the international community," Uzumcu said. "All efforts should be made, by all parties to the conflict, to enable safe access for our team enabling it to conduct its important work." (Additional reporting by Dominic Evans in Beirut and Louis Charbonneau at the United Nations; Editing by Mark Heinrich and Philippa Fletcher)