LONDON — Prime Minister David Cameron said he was worried that Syria's efforts to hand over its chemical weapons arsenal were behind schedule as British diplomats said they planned to raise the matter at the United Nations Security Council on Thursday.

On Wednesday, Syria missed a deadline to hand over all the toxic materials it declared to the world's chemical weapons watchdog, delaying the program for several weeks and jeopardizing a final June 30 deadline.

Cameron, who last August lost a parliamentary vote to authorize British participation in possible air strikes on Syria, expressed his concerns in response to a question from a senior lawmaker.

He said he shared anxiety among British parliamentarians that the Syrian handover program had fallen behind.

"There do seem to be now indications that the program is slowing and that not all the information necessary is forthcoming," Cameron told parliament.

"Britain will continue to put pressure on all parties to make sure the chemical weapons are produced and destroyed."

A Foreign Office spokesman said British diplomats and allies would raise the matter at the U.N. Security Council on Thursday and insist that Damascus meet the final June 30 deadline.

"Syria agreed to the deadlines for removing this material. We recognize that they are challenging but do not accept Syria's excuses for continuing delay," the spokesman said.

"We will raise these delays at the Security Council tomorrow, making clear that Syria needs to meet its obligations."

Cameron raised his concerns about Syria in a phone call with Russian President Vladimir Putin on Monday night, urging him to press Moscow's ally to deliver on its promises.

Alistair Burt, a lawmaker in Cameron's Conservative party and until last October a junior minister responsible for Syrian policy, said stalling by Damascus suggested the chemical deal had been a ploy to avert military action and buy time.

"No surprise that Syrian regime in strong position — chemical deal suited them, and allowed killing to go on," he wrote on the Twitter social media website.