The Syrian government will let a United Nations team of experts visit the site of last week’s alleged chemical weapons attack, state media said Sunday. State TV said the two sides are working to set the date and time of the visit to agreed-upon locations outside Damascus purportedly hit by chemical agents on Thursday, the Washington Post reports.

Reuters reported that a U.N. team is preparing to head to Syria Monday and that the government has promised a ceasefire during the visit.

The opposition says a chemical attack killed hundreds of civilians in rebel-held areas around Damascus took place on Wednesday. The discrepancy in the dates could not be immediately reconciled.

CBS News quoted a “senior U.S. official” saying available evidence at the site in Syria "has been significantly corrupted" and any inspection now would be "too late to be credible."

The Associated Press reported a “senior administration official” said there is "very little doubt" that the Assad regime used a chemical weapon last week. The official said Sunday that U.S. intelligence agencies based their assessment on "the reported number of victims, reported symptoms of those who were killed or injured, and witness accounts."