(CNN) - The United Nations and the United States are calling for an immediate investigation of Syrian activists' claims that the Bashar al-Assad government used chemical weapons in an attack on civilians.
Anti-regime activist groups in Syria say more than 1,300 people were killed in the attack outside Damascus, many of them women and children. Video footage and witness reports appeared to bolster claims that chemical weapons were used.
President Barack Obama has directed the U.S. intelligence community to urgently gather additional information to try to assess whether chemical weapons were used Wednesday, State Department spokeswoman Jen Psaki said Thursday.
At this time, she said, the United States is unable to "conclusively determine" chemical weapons use, but is focused on trying to nail down the facts, along with its international partners.
By Jamie Crawford
The United States sanctioned four senior members of Hezbollah on Thursday for their alleged roles in facilitating terrorist activity in Egypt, Syria, Iraq, Yemen and other countries.
The Lebanon-based Shiite organization, which is a member of the Lebanese government, has already been branded a terrorist group by the United States.
"Whether ferrying foreign fighters to the front lines of the Syrian civil war or inserting clandestine operatives in Europe, the Middle East, and elsewhere, Hezbollah remains a significant global terrorist threat," said David Cohen, Treasury undersecretary for terrorism and financial intelligence.
Those sanctioned include Khalil Harb, who once headed a unit dedicated to terror activities in countries surrounding Israel, Treasury said.