The United States embassy in Algeria has warned about a possible attack by a "terrorist group" on targets in Algiers, possibly near a US-branded hotel in the capital.
A statement on the embassy website told embassy employees to avoid hotels owned or operated by US companies on the July 4 US Independence Day and Algerian Independence Day on July 5.
The warning posted on Wednesday was one of several US security alerts about possible attacks by radical groups.
The US embassy in Uganda warned on Thursday about a "specific threat" of an attack on Entebbe International Airport near Kampala "by an unknown terrorist group".
In the United States, airlines with direct flights arriving from abroad were old to tighten screening of mobile phones and shoes in response to intelligence reports of increased threats from al Qaeda affiliated militant groups, US officials said.
"As of June 2014, an unspecified terrorist group may have been considering attacks in Algiers, possibly in the vicinity of a US branded hotel," said the statement dated July 2 on the Algiers embassy website.
Violence in Algeria has been rarer since the North African state ended its 1990s war with Islamist militants, but al Qaeda in the Islamic Maghreb (AQIM) and other militant groups are still active, especially in the remote south.
Algiers has not seen a major attack for several years, but Islamist militants killed at least 14 Algerian soldiers in April in an ambush in mountains just east of the capital in one of the deadliest attacks on the military in years.
Algeria is concerned about militants using the political chaos in neighbouring Libya as a refuge just across the border.
In January last year, militants raided Algeria's Amenas gas plant near Libya's border, killing 40 oil contractors, all but one of them foreigners, in an attack that prompted British-based BP and Norway's Statoil to pull their workers out.
That attack was carried out by fighters loyal to veteran Algerian militant Mokhtar Belmokhtar.