Syria offering U.N. inspectors access to the site of an alleged chemical weapons attack on a Damascus suburb  was “too late to be credible,” the United States said on Sunday.
“If the Syrian government had nothing to hide and wanted to prove to the world that it had not used chemical weapons in this incident, it would have ceased its attacks on the area and granted immediate access to the U.N. five days ago,” Agence France-Presse reported a senior U.S. official as saying.
The official also told Reuters that “based on the reported number of victims, reported symptoms of those who were killed or injured, witness accounts, and other facts gathered by open sources, the U.S. intelligence community, and international partners, there is very little doubt at this point that a chemical weapon was used by the Syrian regime against civilians in this incident.”
The official added: “We are continuing to assess the facts so the president can make an informed decision about how to respond to this indiscriminate use of chemical weapons .”
Secretary-General Ban Ki-moon’s office said in a statement on Sunday that Syria had promised to observe a ceasefire in Ghouta while a U.N. team begins its “on-site fact-finding activities.”
The Syrian Foreign Ministry said Sunday in a statement broadcast on state television that “an agreement was concluded today [on Sunday] in Damascus between the Syrian government and the United Nations during the visit of the U.N. high representative for disarmament, Angela Kane, to allow the U.N. team, lead by Professor Aake Sellstroem, to investigate allegations of chemical weapons use in a Damascus province,” AFP reported.
The agreement “is effective immediately,” added the ministry.
Russia, meanwhile, welcomed Syria’s offer to allow the U.N. access to the alleged attack site, warning the West that military action against the Syrian regime would be a “tragic mistake.” 
“We strongly urge those who, by attempting to impose their own results on the U.N. experts, are raising the possibility of a military operation in Syria to use their common sense and refrain from committing a tragic mistake,” AFP quoted the Foreign Ministry Spokesman Alexander Lukashevich as saying.
The alleged chemical weapons attack on Ghouta last week killed hundreds of civilians. Both the opposition and the Syrian regime blame each other regarding who carried out the attack.
On Saturday, the Syrian opposition said that the government was “lying” when it accused rebels of carrying the chemical attack, while Damascus said it found chemical materials that had been used by rebels stored in tunnels in the capital.
Meanwhile, Abu Mohammed al-Golani, head of Jabhat al-Nusra an al-Qaeda-linked rebel group operating in Syria, vowed on Sunday to attack villages home to President Bashar Assad’s minority sect to avenge the attack on Ghouta, The Associated Press reported.
Al-Golani’s comments were relayed in an audio recording posted on a militant website that usually carries al-Qaeda’s statements.