The White House says it has conclusive evidence that Syrian President Bashar Assad's regime has used chemical weapons against opposition forces seeking to overthrow the government. That crosses what President Barack Obama has called a ``red line'' that would trigger greater American involvement in the crisis.

Administration officials say Obama is considering both political and military options, but suggest deeper involvement may not be imminent.

The administration estimates that 100 to 150 people have died from chemical weapons attacks in Syria. The White House blames the Syrian government for the attacks and says the casualty data is likely incomplete. It says it has no reliable, corroborated information to suggest that the Syrian opposition in the country's civil war has acquired chemical weapons. (Associated Press)