A mortar slammed into a ninth-grade classroom in Damascus on Tuesday and killed 29 students and a teacher. State media SANA blamed the attack on terrorists, a term used to describe rebels who are trying to topple President Bashar Assad's government, The Associated Press reported. The mortar hit the al-Batiha school in al-Wafideen camp 15 miles northeast of Damascus, according to SANA. The violence comes on the heels of news that U.S. intelligence has detected movement in the regime's chemical weapons stock. Secretary of State Hillary Clinton warned Syria on Monday that use of chemical weapons against rebels would be a "red line" prompting action from the U.S. Syria is believed to have hundreds, if not thousands, of tons of chemical agents, experts say. The Damascus suburbs have been an opposition stronghold since the uprising against Assad began in March 2011 and the scene of heavy fighting since last week. Assad's forces have so far repelled major rebel advances on the capital, though their hold may be slipping.