(Adds details about closed-door briefing; quotes from British and Russian envoys, U.N. chief; background)
By Louis Charbonneau and Michelle Nichols
UNITED NATIONS, Feb 6 (Reuters) - The head of an international chemical weapons mission in Syria told the U.N. Security Council on Thursday that accelerated cooperation by the Syrian government is vital as a June 30 deadline looms for destruction of the country's toxic arsenal, a diplomat said.
Sigrid Kaag, head of the joint mission of the United Nations and the Organization for the Prohibition of Chemical Weapons, briefed the 15-member council behind closed doors one day after Syria failed to meet an OPCW deadline for having transferred all its chemicals out of the country.
"With deadline on the horizon, it is essential that Syria accelerates" shipments of toxic chemicals out of the country, said Kaag, according to a diplomat at the briefing who spoke on condition of anonymity. "Time for action is now."
Kaag's briefing is crucial as the council considers whether the Syrian government - which is locked in a three-year-old civil war with rebels intent on toppling it - could eventually be found in non-compliance with an international demand that it eliminate its chemical weapons program by June 30.
U.N. Secretary-General Ban Ki-moon said earlier on Thursday he was confident Syria would meet the end-June deadline as agreed under a U.S.-Russian plan made legally binding in a Security Council resolution last year.
Syria has missed the Feb. 5 deadline to ship abroad its entire stockpile of chemicals, prompting fears it could fail to fulfill on time the plan that helped avert a threatened U.S.-led missile strike against President Bashar al-Assad's government.
Britain's U.N. ambassador, Mark Lyall Grant, told reporters before Kaag's briefing that "the time for excuses has run out."
"Everything is in place and there needs to be proper arrangements for accelerating the process of getting the chemicals out of Syria," he said. "The international community has bent over backwards."
"We're now waiting for the Syrian regime to allow faster movement of chemicals out of the country," Lyall Grant said.
Russia, Assad's main diplomatic protector in the Security Council, suggested on Wednesday that the Syrian government appeared to have the situation under control.
"They're now in a good place as far as this program is concerned," Russian U.N. Ambassador Vitaly Churkin told reporters.
"The Syrian government has done a couple of runs already," he said. "They are working very hard to be as technically prepared as humanly possible and still complaining that they are missing some technical support which they require but we believe that generally the main components are there."
Russia said earlier this week that Assad's government was prepared to complete the transfer of its chemical stockpiles abroad by March 1.
According to a second diplomat at Thursday's briefing, Kaag told the council that Syrian authorities have sufficient material to carry out ground movements.
Ban said in a report last month that Syria has enough equipment to transfer the chemicals out of the country.
In addition to unfulfilled requests for equipment, Syria has blamed the delays on security concerns and the weather. (Editing by Nick Zieminski and Mohammad Zargham)