Secretary of State John Kerry said Sunday the United States had evidence that Syria's government used the nerve agent sarin in an Aug. 21 attack on the outskirts of Damascus.
Hair and blood samples from victims of the attack have "tested positive for signatures of sarin," Kerry said in a series of interviews with U.S. television networks.
The attack killed 1,429 people, U.S. officials say.
"In the last 24 hours, we have learned through samples that were provided to the United States and that have now been tested from first responders in East Damascus, and hair samples and blood samples have tested positive for signatures of sarin," Kerry said on NBC's Meet the Press.
President President Bashar Assad, meanwhile, said Sunday that Syria would continue its "fight against terrorism" despite threats of military action by the United States.
"Syria is capable of dealing with any kind of foreign aggression, just as it does with internal aggression, and will achieve victories to regain the security and stability of the country," the president said.
U.S. President Barack Obama said Saturday he had decided on "military action" against Syria but would seek congressional approval first.
"After careful deliberation, I have decided that the United States should take military action against Syrian regime targets," Obama, accompanied by Vice President Joe Biden, said in the White House Rose Garden.
Obama gave no specific date for the strike, saying it would occur when Washington decides.
Congress is currently on summer recess, but is scheduled to return to session on Sept. 9.
The U.S. government released a report Friday stating that a chemical weapons attack was staged on Aug. 21 in Ghouta that killed 1,429 people, including 426 children.
U.N. inspectors in Syria to investigate the Aug. 21 incident and other alleged chemical weapons attacks left the country Saturday.
Britain's House of Commons voted 285-272 last week against a motion that would have opened the door to that country's participation in a U.S.-led strike, but France said it remained "prepared" to participate in a punitive action against Syria.
More than 92,000 people died in Syria's internal conflict between March 2011 and April 2013, according to a report released in June by the U.N. Office of the High Commissioner for Human Rights. EFE