U.S. President Barack Obama and British Prime Minister David Cameron on Friday expressed "grave concern" in a phone call about the alleged use of chemical weapons in Syria.

Obama and Cameron spoke "on the shared security challenges faced by the United States and the United Kingdom, including continued violence in Syria," the White House said in a statement.

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," it said.

They would continue to consult closely regarding this incident, as well as possible responses by the international community to the use of chemical weapons, it added.

A spokesman for Cameron said that the two leaders "reiterated that significant use of chemical weapons would merit a serious response from the international community and both have tasked officials to examine all the options."

Syrian opposition charged the government forces of killing 1,300 people in recent chemical attacks, which was denied by the Syrian government.

The allegation came just two days after a group of UN inspectors began a probe into alleged use of chemical weapons in Syria in March.