The head of the mission charged with destroying Syria's chemical weapons says the government has accelerated its efforts after several missed deadlines and that March will be critical if the country is to completely eliminate its stockpiles by the June 30 deadline.

Sigrid Kaag told reporters after briefing the U.N. Security Council behind closed doors Wednesday that about one third of Syria's chemical weapons material has been removed or destroyed and "in the next few days we expect to reach already 40 or 41 per cent."

She said Syrian authorities submitted a revised timeline that would complete the removal and destruction in the country between the middle and end of April.

Kaag said that would be "in time, should all go well, to meet the overall deadline of June 30."