Yemeni authorities in Sana'a prevented a bomb attack on a car carrying four U.S. Embassy personnel, the U.S. State Department reported Thursday.

On Wednesday, police caught a Jordanian citizen as he attempted to plant explosives next to the car, which was stopped near a pizza restaurant frequented by Westerners. No one was injured. The attacker was carrying fake papers and had weapons in his car. Yemeni police are trying to determine whether the man has any links to al-Qaida.

In Pakistan, another U.S. public official serving abroad saw himself caught in a dangerous situation this week. Islamabad's C.I.A. station chief left the country Thursday, after his life was threatened when a document revealing his name was made public as part of a lawsuit over alleged U.S. drone attacks. The C.I.A. official served in an important undercover role, managing the use of drones against al-Qaida and the Taliban in Pakistan.

The threats against the chief "were of such a serious nature that it would be imprudent not to act," an unnamed U.S. official said.

Back in the United States, law enforcement is ramping up domestic security measures, including implementing random baggage checks for passengers boarding the D.C. Metro. A joint FBI and Homeland Security bulletin issued Wednesday warned that "terrorists may seek to exploit the likely significant psychological impact of an attack targeting mass gathering in large metropolitan areas during the 2010 holiday season." However, the bulletin noted that "the timing of a terrorist attack" is determined more by the "terrorists' readiness to execute an attack rather than a desire to attack on a specific date."

The bulletin mentioned other plots for law enforcement to consider in trying to prevent holiday season attacks. Last year, Nigerian Umar Farouk Abdulmutallab tried to set off a bomb on board a Detroit-bound airliner on Christmas Day. The Yemeni-based al-Qaida group, Al-Qaida in the Arabian Peninsula, claimed credit for the attack. Last month, Mohamed Osman Mohamud was arrested after an FBI sting operation ended in the Somali man's attempted bombing of a Christmas-tree lighting ceremony in Portland, Oregon.

The bulletin comes after Iraqi authorities announced Wednesday that captured insurgents confessed al-Qaida is planning attacks around Christmas-time in the United States. The advisory did not mention the insurgents' claims.