Secretary of Defense Chuck Hagel says the U.S. is "concerned" that Syria is behind schedule in removing its chemical stockpiles.

Hagel, speaking during a visit to Poland, says Syria "is behind in delivering these chemical weapons precursor materials on time with the schedule that was agreed to."

White House spokesman Jay Carney, speaking to reporters aboard Air Force One, added: "It is the Assad regime's responsibility to transport those chemicals to facilitate removal. We expect them to meet their obligation to do so."

The remarks came on the same day that the Organization for the Prohibition of Chemical Weapons, or OPCW, the international watchdog overseeing the destruction of Syria's chemical weapons in line with an agreement forged last year, discussed with U.N. Secretary-General Ban Ki-moon the need "for the removal process to pick up pace."

NPR's Michele Kelemen says the U.S. believes that less than 5 percent of the most dangerous chemicals have been moved out of Syria to date.

In a statement issued by the Robert P. Mikulak, the U.S. representative at the OPCW, said:

"Today we are one month past the 31 December completion date set by the Council. Almost none of the Priority One chemicals have been removed, and the Syrian government will not commit to a specific schedule for removal. This situation will soon be compounded by Syria's failure to meet the February 5th completion date set by this Council for the removal of all Priority Two chemicals. ...

"Syria has said that its delay in transporting these chemicals has been caused by 'security concerns' and insisted on additional equipment — armored jackets and shipping containers, electronic countermeasures, and detectors for improvised explosives devices. ... These demands are without merit and display a 'bargaining mentality' rather than a security mentality."

Concern about the pace of disposing of Syria's stockpiles comes as Human Rights Watch accused the Syrian regime of "deliberately and unlawfully" demolishing thousands of homes in opposition strongholds in the capital, Damascus.

In a report, the group shows before and after satellite imagery of areas where whole blocks have been razed.

"Wiping entire neighborhoods off the map is not a legitimate tactic of war," says Ole Solvang, an HRW emergencies researcher was quoted by the BBC as saying. "These unlawful demolitions are the latest additions to a long list of crimes committed by the Syrian government."

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