The statement, the second such message since twin bombings in Algiers last month claimed by al Qaeda, added that all Americans in Algeria were advised to limit their movements around the country, the embassy message, dated January 18, said.

"In response to continuing indications of possible terrorist attacks in Algiers, the Embassy has instructed its employees to avoid non-essential movements around the city until further notice, and may occasionally restrict movement completely," the message posted on the embassy Web site said.

Al Qaeda in the Islamic Maghreb claimed responsibility for a suicide bombing of U.N. buildings in Algiers on December 11 and another attack the same day which killed a total of at least 41 people, according to officials, including 17 U.N. employees.

The U.S. embassy issued a similar message on December 23 announcing restrictions on the movement of its staff in the capital. Up to 1,000 Americans live in Algeria, many of them working in oil and gas fields in the Saharan south.

Britain advised its citizens last Wednesday against all but essential travel to the capital of the OPEC member state, without elaborating.

Previous British advice did not warn specifically against travel to the port city, focusing instead on troubled areas to the east of the city where clashes periodically take place between security forces and Islamist armed groups.

Algerian Islamist rebels aligned themselves with Al Qaeda last year and began copying its tactics by carrying out a string of high-profile urban suicide bombings.

The group was previously called the Salafist Group for Preaching and Combat and preferred to ambush government security forces from its main base in the Kabylie region east of Algiers.

The police, as well as the paramilitary police force which works for the Defence Ministry, have stepped up security in and around the capital of three million since the start of the year.