From the U.S. State Department:

The Department of State urges U.S. citizens to avoid all travel to Lebanon because of current safety and security concerns. U.S. citizens living and working in Lebanon should understand that they accept risks in remaining and should carefully consider those risks. This supersedes the Travel Warning issued on May 8, 2012, to emphasize information on security, kidnappings, and an upsurge in violence in Lebanon and the region.

The potential in Lebanon for a spontaneous upsurge in violence remains. Lebanese government authorities are not able to guarantee protection for citizens or visitors to the country should violence erupt suddenly. Access to borders, airports, roads, and seaports can be interrupted with little or no warning. Public demonstrations occur frequently with little warning and have the potential to become violent. Family or neighborhood disputes often escalate quickly and can lead to gunfire or other violence with little or no warning. The ability of U.S. government personnel to reach travelers or provide emergency services may be severely limited. ...

U.S. State Department Warning