Syria will allow UN inspectors to visit a site near Damascus where an alleged chemical weapons attack is said to have killed hundreds of people, state media report.
The move came shortly after a senior US official told reporters there was "very little doubt" that a chemical weapon had been used by government forces.
Activists say Syrian forces killed more than 300 people in several suburbs east and west of the capital on Wednesday.
The Syrian authorities have denied any responsibility and blamed "terrorists".
Earlier, Syria\’s information minister warned that US military intervention would bring chaos and that the Middle East would "burn".
Omran Zoabi told Lebanon-based al-Mayadeen TV the Syrian state and its armed forces remained strong, with friends and allies in the region.
The U.S. defense secretary says the military is prepared to take action against Syria, if President Barack Obama decides to take such action.
Chuck Hagel said Sunday during a visit to Malaysia that Washington and its allies are still assessing how to react to the evidence of chemical weapons being used in Syria.
Top U.S. military and national security advisors presented President Obama with a detailed set of options Saturday for responding to the Syrian government\’s alleged use of chemical weapons.
A White House statement said the president also conferred with British Prime Minister David Cameron as the U.S. intelligence community continues to gather facts on the situation. Both men voiced "grave concern" about the weapons allegations.
The White House security meeting, attended by Vice President Joe Biden, CIA Director John Brennan and National Security Advisor Susan Rice, comes just days after accusations that hundreds of people were killed near Damascus in a chemical weapons attack.
U.S. State Department officials say Secretary of State John Kerry has discussed the issue with his Syrian counterpart and other top officials in the region. Kerry told Syrian Foreign Minister Walid al-Moallem Thursday that if Damascus has nothing to hide, then it should allow "immediate and unimpeded" U.N. access to the site rather than block investigators.
Kerry also spoke Saturday with officials from the Arab League, Saudi Arabia, Jordan, the United Arab Emirates and Turkey to emphasize "the importance of quickly determining the facts" of chemical weapons use in Syria.
The international medical relief group Doctors Without Borders said Saturday three Damascus hospitals have received about 3,600 patients displaying symptoms of exposure to neurotoxic agents.
The symptoms included convulsions and blurred vision, and the doctors\’ group said nearly 10 percent of those patients have died. Some of the medical and first aid workers treating the people brought in for medical care also found themselves contaminated.
The relief group said the overall situation strongly indicates the local population suffered "mass exposure to a neurotoxic agent," which it said "would constitute a violation of international humanitarian law."
Syria\’s main ally Russia said there was evidence rebels were behind the attack.
Russia\’s Foreign Ministry Friday said claims by Syria\’s opposition that hundreds died in a poisonous gas attack several days ago should undergo an objective investigation, and it called on Syria to cooperate.
Moscow also called on rebel forces to guarantee safe passage for U.N. investigators who are already in the country looking into previous allegations of chemical use. The ministry released the statement following a call between Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry.
Last year, President Obama said the use of chemical weapons in Syria would cross a "red line" and force a tough US response.
Assad\’s government has consistently denied using chemical weapons. It has accused the opposition of using chemical weapons earlier this year near Aleppo. The U.N. team already on the ground in Syria was sent to investigate those claims.
Syria has been embroiled in a war for more than two years, during which more than 100,000 people have been killed and millions have been displaced or become refugees in other countries, according to the United Nations.