Their comments echoed remarks made Friday by a Russian diplomat, Mikhail Ulyanov, after an international meeting on the chemical arms removal effort. Mr. Ulyanov, the head of the Russian foreign ministry’s disarmament department, said, “The removal has not yet begun,” according to the Russian news agency RIA Novosti.

The government of President Bashar al-Assad has until mid-2014 to destroy its chemical weapons program under a deal struck by Russia and the United States in September. To meet that challenging timetable, it agreed with the watchdog group, the Organization for the Prohibition of Chemical Weapons, to remove more than 500 metric tons of its most toxic chemicals by the end of this year and the remaining 700 tons of chemicals in its stockpile by early February.

The organization warned of possible delays when it approved the plan, and the statement issued on Saturday noted the “important progress” Syria has made in dismantling its chemical weapons program in the past three months. Three weeks ago, the head of the group, Ahmet Uzumcu, acknowledged that meeting the deadline would be “quite difficult.”

American officials have acknowledged the particular challenges of moving dangerous chemical weapons across a landscape torn by civil war, and took the news of the delay in stride. “This was always going to be complex,” a senior administration official said in Washington on Sunday, referring to the deadlines as “milestones” instead. “We’re going to work with international partners to keep this on track and to keep up the pressure on the Assad regime to meet its commitments.”

The plan the group agreed to this month called for Syria to transport the critical chemicals, including 20 tons of sulfur mustard and precursors for making sarin and VX nerve gas, from 12 storage sites around the country to Latakia. Danish and Norwegian ships are to then take them under naval escort to an Italian port for transfer to an American vessel fitted with special equipment for destroying them at sea.