In a statement, White House spokesman Josh Earnest said the United States is "deeply concerned" by reports of the deadly attack outside the Syrian capital, Damascus, and is working to gather information.
"The United States strongly condemns any and all use of chemical weapons. Those responsible for the use of chemical weapons must be held accountable," Earnest said.
Activists accused the Syrian government of firing rockets with poisonous gas on homes early Wednesday, killing civilians in their sleep. Images posted online showed bodies wrapped in white sheets lined up on the ground. Women and children appeared to be among the dead. The images on the Web could not be independently verified.
The official Syrian news agency called the reports "untrue."
A team of U.N. inspectors is already in Syria to investigate previous charges of chemical weapons use in the more than 2-year-old civil war between the government of President
The U.N. inspectors are charged with documenting and confirming allegations of attacks, not determining responsibility.
The White House said Wednesday it believed the U.N. team was prepared to investigate the latest claim "and that is consistent with its purpose and mandate."
"For the U.N.'s efforts to be credible, they must have immediate access to witnesses and affected individuals, and have the ability to examine and collect physical evidence without any interference or manipulation from the Syrian government," Earnest said. "If the Syrian government has nothing to hide and is truly committed to an impartial and credible investigation of chemical weapons use in Syria, it will facilitate the U.N. team's immediate and unfettered access to this site."
Earnest said the White House had called on the U.N. Security Council to review the allegations.
"The United States urges all Syrian parties, including the government and opposition, to provide immediate access to any and all sites of importance to the investigation and to ensure security for the U.N. investigative team," Earnest said.