Syria agreed Sunday to give UN inspectors full access to the site of a purported chemical weapons attack amid accusations of a cover-up by White House officials.
The decision, first reported by AFP and CNN, is effective immediately.
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It came shortly after a senior US official told reporters there was "very little doubt" that chemical weapons had been used by government forces last week in an attack that activists say killed more than 300 people in a Damascus suburb.
Syrian authorities have denied any responsibility and blamed "terrorists" for any such attack.
The US official, who spoke anonymously to The Associated Press, said the White House believed the Syrian government was barring UN investigators from the site to allow evidence of any kind of attack to degrade.
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Syria, meanwhile, warned against the United States taking any military action over the suspected nerve gas attack.
"U.S. military intervention will create a very serious fallout and a ball of fire that will inflame the Middle East," Syrian Information Minister Omran Zoabi was quoted by state news agency SANA as saying to Lebanon-based al-Mayadeen TV.
President Bashar al-Assad's closest ally, Iran, also warned against the US crossing the "red line" in Syria's civil war.
The developments came one day after the government claimed to find chemical agents in rebel tunnels in a Damascus suburb, saying several soldiers were overcome by the fumes and had to be taken away via ambulance.