WASHINGTON (AFP) - US President Barack Obama and British Prime Minister David Cameron spoke Saturday and expressed their "grave concern" about the reported use of chemical weapons by the Syrian regime against civilians.

A White House statement said the two leaders "will continue to consult closely" regarding the alleged attack near Damascus on Wednesday, "as well as possible responses by the international community to the use of chemical weapons."

Notification of the call between Obama and Cameron came shortly after another statement regarding the US president's meeting with top aides in his National Security Council on Saturday, which appeared to give credence to reports of the chemical attack on rebel-held areas near the Syrian capital.

"In coordination with international partners and mindful of the dozens of contemporaneous witness accounts and record of the symptoms of those killed, the US intelligence community continues to gather facts to ascertain what occurred," the White House said.

"The president also received a detailed review of a range of potential options he had requested be prepared for the United States and the international community to respond to the use of chemical weapons," it added.

The meeting came a day after US Secretary of Defense Chuck Hagel said the military had presented options to Mr Obama and was moving forces into place ahead of any possible decision.

Mr Obama has so far voiced caution, warning that a hasty military response could have unforeseen consequences, including embroiling the United States in another prolonged Middle East conflict.

But he is under mounting pressure to act following reports of the alleged chemical weapons attack, which Doctors Without Borders said had killed 355 people, due to "neurotoxic" symptoms.

Opposition groups say the reported attack was carried out by Syrian President Bashar al-Assad's forces and that it killed more than 1,000 people.