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 has denied all allegations of chemical weapons use. State-controlled media have claimed it was rebel forces that carried out nerve gas attacks. The state news agency SANA reported that soldiers found evidence of this while searching tunnels in Damascus used by "armed terrorists."
The United States and other world powers have been pushing for a U.N.-led investigation of the chemical weapons allegations. A top U.N. official arrived in Damascus Saturday to push for access to the site where rockets loaded with poison gas were allegedly launched.
Syrian opposition leaders and activists have released video of large numbers of bodies - many of them young children - that bear no signs of physical violence. Those pictures, and separate scenes from hospitals showing patients writhing in agony without apparent wounds - are said to be persuasive indications that they were victims of an attack that used nerve gas or some other deadly chemical agent.
Iran's new president, Hassan Rouhani, condemned the use of chemical weapons in Syria, but state-controlled Iranian media report he did not blame either side in comments Saturday. Iran is Syria's ally, and its Foreign Ministry has previously said evidence indicates that Syrian rebels launched the attack.