U.S. President Barack Obama on Sunday conversed with his French counterpart Francois Hollande over phone to discuss possible coordinated response to the alleged chemical weapons use by Syrian government forces.

"The two leaders expressed their grave concern about the reported use of chemical weapons by the Syrian regime against civilians near Damascus on Wednesday, August 21," the White House said in a statement.

"President Obama and President Hollande discussed possible responses by the international community and agreed to continue to consult closely," said the statement, without disclosing further details.

The call is part of the Obama administration's ongoing efforts to rally international support for a possible military response to the Syrian government amid rising political pressure both at home and abroad.

Obama on Saturday called British Prime Minister David Cameron to discuss "the shared security challenges" faced by the two close allies, including the continued violence in Syria.

They expressed their "grave concern" about the reported chemical attack by the Syrian government troops and agreed to continue to consult closely regarding this incident, as well as possible responses by the international community to Syria, according to a White House statement Saturday.

In Paris, the French President's Office issued a statement Sunday, saying the French leader told Obama that everything indicates that the Syrian government was "the perpetrator of these unacceptable attacks."

The two leaders agreed to stay in close contact so as to produce a joint response to "this unprecedented aggression," the statement added.

France and Britain, both permanent members of the United Nations Security Council, have been the lead supporters of a series of U.S.-led military operations overseas in recent years, including the wars in Iraq and Afghanistan and the 2011 NATO bombing of Libya.

Coupled with reports that the Obama administration is considering possible military intervention in Syria, the U.S. Navy has sent a fourth warship armed with cruise missiles into the eastern Mediterranean Sea.

Also on Saturday, Obama convened a meeting of his national security team to assess the latest intelligence concerning the alleged chemical attack in Syria, and discuss the options of possible U.S. and international responses.

White House officials said the U.S. has a range of options available, ranging from a cruise missile strike to a more sustained air campaign against Syria, and will act "very deliberately" so as to make decisions consistent with the U.S. national interests and assessment on how to advance its objectives in Syria.

In Moscow, Russian Foreign Ministry spokesman Alexander Lukashevich on Sunday warned Western countries against rushing to conclusion on the chemical weapons use in Syria pending the investigation by a UN inspection team.

Welcoming Syria's decision to allow UN experts to examine the site of the alleged chemical attack in eastern suburbs of Damascus, Lukashevich urged the international community to show patience and wait for the results of the UN investigation.

"Serious attention has been paid in Moscow to a statement by U.S. Defense Secretary Chuck Hagel about measures, ordered by President Barack Obama, to make American armed forces ready for armed action against Syria at any moment," said Lukashevich in a statement.

Moscow believed that the current fuss about the alleged use of chemical weapons "clearly aims to interfere with the work of UN independent chemical weapon experts that has begun successfully."

The diplomat also said it was "reminiscent of events of 10 years ago in which, using false information that the Iraqis possessed weapons of mass destruction as a pretext and bypassing the United Nations, the United States launched a reckless attack with consequences that everyone is well aware of."

He warned that any unilateral armed action that bypassed the UN would "undermine international efforts to find a political and diplomatic solution to the Syrian conflict ... and have an extremely destructive effect on what already is an explosive situation in the Middle East."

The Syrian opposition claimed that 1,300 people were killed in a government chemical weapons attack on militant strongholds in the suburbs of Damascus last Wednesday. The Syrian government denied the allegation.

The Syrian civil war, which began in March 2011 between government forces and armed opposition seeking to oust President Bashar al-Assad, has led to the deaths of more than 93,000 people and forced more than 1.7 million people to flee the country.