From the U.S. State Department:

The Department of State continues to warn U.S. citizens against travel to Syria and strongly recommends that U.S. citizens remaining in Syria depart immediately. This Travel Warning supersedes the Travel Warning dated August 1, 2012, to remind U.S. citizens that the security situation remains volatile and unpredictable throughout the country, with an increased risk of kidnappings, and to update contact information.

No part of Syria should be considered immune from violence, and the potential exists throughout the country for hostile acts, including kidnappings.

Communications in Syria are difficult as phone and Internet connections have become increasingly unreliable. The Department of State has received reports that U.S. citizens are experiencing difficulty and facing dangers when trying to leave Syria via land borders, and that seats on flights out of Syria are becoming increasingly scarce.

The U.S. Embassy in Damascus suspended its operations in February 2012 and therefore cannot provide protection or routine consular services to U.S. citizens in Syria. The Government of the Czech Republic, acting through its Embassy in Damascus, serves as Protecting Power for U.S. interests in Syria. The range of consular services the Czech Republic provides to U.S. citizens is extremely limited, and those services may require significantly more processing time than at U.S. embassies or consulates outside of Syria. Neither U.S. passports nor visas to the United States are issued in Syria. ...

U.S. State Department Warning