The United States on Monday warned of a possible terrorist attack against US interests in Yemen this week and said it was temporarily closing its embassy in Sanaa to the public.
In a notice to US citizens in Yemen, the embassy said it had information that an attack might occur on or about Tuesday. The notice was made available to AFP in Washington by the State Department.
"The embassy has received information that a terrorist attack against US interests in Yemen might occur on or about April 23, 2002," it said.
"While there are no details as to the possible target in Yemen, the embassy is taking a number of additional security measures," the notice said.
"Embassy Sanaa is temporarily suspending immigrant visa and routine American citizen services to the public on Tuesday, April 23, 2002," it said. "The embassy will be open to emergency American citizen services only."
The notice, which urged Americans in Yemen "to keep a low profile, vary routes and times of travel, and avoid large crowds and demonstrations," gave no further details of the possible threat.
However, the warning comes amid large anti-US and -Israel demonstrations in Yemen over the current Middle East crisis.
It also follows the release of a message from a hitherto unknown group calling itself "Sympathizers of the al-Qaeda Organization," the terrorist group headed by Saudi-born Osama bin Laden, claiming responsibility for a series of recent explosions in Yemen.
The "Sympathizers of the al-Qaeda Organization" also threatened to carry out suicide bombings unless Yemeni authorities released 173 militants.
In an April 10 e-mail, the group said it was behind an April 4 blast near Yemeni intelligence headquarters in Sanaa and two attempted bomb attacks against the homes of intelligence officers.
The group vowed to carry out "martyrdom operations (suicide attacks) against premises of the intelligence service in all provinces and senior political figures" unless the militants it said were held at intelligence headquarters were freed within 30 days.
"The only accusation against the 173 is that they belong to the al-Qaeda organization," which the United States has blamed for the September 11 attacks on New York and Washington, the statement said.
Bin Laden's family, which owns an extremely successful Saudi construction firm, originally hails from Yemen.
Two days after the message was released, a bomb exploded in a neighborhood adjacent to the US embassy in Sanaa, prompting Yemeni authorities to step up security there.
On April 16, a bomb exploded in the center of Sanaa, blowing in the front of the civil aviation headquarters.
The three explosions followed a March 15 grenade attack on the US embassy in Sanaa that police said was an isolated incident perpetrated by a mentally disturbed man.
US officials have been on high alert in Yemen since an October 2000 suicide attack blamed on al-Qaeda on the USS Cole, a naval destroyer, in the port of Aden killed 17 sailors and injured 39 others.
The Cole, which was hit by a small boat laden with explosives, left the 8,300-tonne destroyer in need of 250 million dollars in repairs.