Spokesman Larry Schwartz said: "The embassy received a credible and specific threat. As a result the ambassador decided it would be prudent to close the embassy for the day."

BBC's Paul Adams: "American embassy officials are not saying much"

"We will discuss the threats with the appropriate authorities," he added, refusing to say if the threat came from an individual or an organisation.

Israeli radio said the threats were aimed at US Ambassador Ned Walker. Israeli border police and anti-terrorist units were deployed around the embassy.

Embassy staff were told not to turn up for work. The embassy will also be closed as planned on Friday, New Year's Day, and over the weekend.

Embassy alerts

BBC Correspondent Paul Adams says this is the first threat directed against the embassy in Tel Aviv since bombs destroyed the US missions in Nairobi and Dar-es-Salaam in August.

US diplomatic missions have been on alert ever since.

The recent American-led bombing campaign against Iraq has also triggered fresh expressions of anti-American sentiment in a number of Arab capitals.

In Syria, the American Embassy was attacked and parts of it ransacked.

The United States ordered a two-day closure of most of its embassies in Africa during the recent air strikes on Iraq , with only those in South Africa, Nigeria and Burkina Faso staying open.

And in the run-up to Christmas, American embassies around the Gulf issued a warning to their citizens in the region about "the strong possibility" of terrorist attacks on US interests over Christmas or the Muslim holy month of Ramadan.

American citizens in the Gulf region have been told to be extra vigilant during the month of Ramadan.