The US State Department in a statement said "the security threat to all US citizens in Yemen remains high due to continuing efforts by al-Qaida to re-constitute an effective operating base there".
"This could lead to possible attacks by extremist individuals or groups against US citizens, facilities, businesses and perceived interests," it said in the alert, which warned its citizens to avoid all travel to Yemen.
Yemen has been the subject of a series of US advisories and warnings since the October 2000 bombing of the destroyer USS Cole, which killed 17 sailors. The State Department has constantly reiterated its position that the possibility of attacks on US citizens remains high.
"The security threat to all US citizens in Yemen remains high due to continuing efforts by al-Qaida to re-constitute an effective operating base” in Yemen.
US State Department
In the previous major advisory on 1 December 2002 the State Department had warned its citizens against travelling to Yemen because of threats following a suicide bombing at a resort in Kenya.
In that advisory, the department had also advised travellers of an increased risk of “terrorist attacks'' in east Africa, particularly Djibouti, where US forces were then training for anti-terrorist operations.
The advisory came in the immediate aftermath of a suicide bombing at a resort hotel in Mombasa, Kenya, which left 16 people dead, including three bombers. The same day, attackers armed with shoulder-fired missiles attempted to shoot down an Israeli charter plane as it look off from Mombasa.
Yemen is the ancestral home of bin Ladin, and this is said to another reason for US repeat advisories to its citizens. According to some US officials, Usama bin Ladin may have sought refuge in Yemen following the US invasion of Afghanistan and the fall of the Taliban.