The alert is issued because of an al-Qaeda terrorist threat. The State Department says the potential for terrorism is particularly strong in the Middle East and North Africa.
A consortium that deals with security issues is warning about possible threats to oil installations in Libya.
Oil rose on Thursday as financial markets got a boost from improving U.S. economic data showing jobless claims fell to a five-year low and housing starts rose sharply.
Twenty-five foreign hostages escaped and six were killed on Thursday when Algerian forces launched an operation to free them at a remote desert gas plant, Algerian sources said, as one of the biggest international hostage crises in decades unfolded.
Global oil markets, under pressure from increased North American production, are facing the return of a familiar upside risk - the threat of supply disruption from North Africa after an attack on an Algerian gas field swiftly escalated into an international hostage crisis.
President Francois Hollande travels to Algeria on Wednesday to try to heal wounds left by a bloody war half a century ago and to seek greater access to the former colony's oil wealth.
“Al Qaeda is more dangerous now than ever before,” said Rep Peter King, on The Kudlow Report. “Al Qaeda has not been decimated.”