A senior administration official says there is "very little doubt" that a chemical weapon was used by the Syrian regime against civilians in an incident that killed at least a hundred people last week.

The official says Sunday that the U.S. intelligence community based its assessment given to the White House on "the reported number of victims, reported symptoms of those who were killed or injured, and witness accounts." The official spoke on condition of anonymity because the official was not authorized to speak publicly.

The official says the White House believes the Syrian government is barring a U.N. investigative team immediate access to the site of a reported Aug. 21 chemical attack in the Damascus suburbs in order to give the evidence of the attack time to degrade. Syria later agreed to allow UN inspectors to visit the site of last week's possible attacks.

Hagel: US Still Weighing Response To Syria

U.S. Defense Secretary Chuck Hagel says the Obama administration is still weighing the question of whether to use military force in Syria in response to a purported chemical weapons attack.

Secretary of Defense Chuck Hagel (Alex Wong/Getty Images)

Speaking to reporters Sunday in the Malaysian capital of Kuala Lumpur, Hagel declined to say what action the U.S. might take.

He said the administration is weighing many factors. These include an intelligence assessment of the attack in Syria, as well as what he called legal issues and the matter of international support for any military response.

Hagel is in Malaysia to start a long-planned one-week Asia tour, even as he remains in contact with Washington about unfolding events in Syria.