(CBS) The U.S. Immigration and Naturalization Service has ordered that all Yemeni nationals be searched before entering or leaving the United States.

CBS News Correspondent Bob Orr reports it is one of the most specific security alerts to be issued since September 11th.

An INS memo obtained by CBS News directs agents at U.S. airports, borders, and ports to do: "A complete and thorough search of all baggage" carried by Yemeni travelers and make "An inventory of all effects." Only those carrying diplomatic passports are exempt.

The memo specifically orders agents to look for "...large sums of currency, thermos bottles, night vision goggles or devices." It warns, "under no circumstances will an inspecting officer open a thermos bottle."

The order was given last Thursday after a recent raid of an apartment housing a number of Yemeni nationals somewhere in the Northeast.

Law enforcement officers discovered dozens of thermos bottles, some rigged with batteries; wire was also found. Authorities say these components could have been used in manufacturing bombs.

One source said the recovery of the materials and the ensuing alert are not connected to any known plot or specific threat. Officials haven't said whether anyone has been detained as a result of this latest security memo.

Yemen has been a known haven for al Qaeda operatives.

The guided missile destroyer USS Cole was badly damaged in a bombing in the Yemeni port of Aden, on Oct. 12, 2000, when a small boat laden with explosives was detonated beside the warship.

Seventeen U.S. sailors were killed and 39 others were injured in the attack, blamed on Saudi-born militant Osama bin Laden's al Qaeda guerrilla network. The United States also blames bin Laden and al Qaeda for the Sept. 11 attacks on the United States that killed more than 3,000 people.