The US Embassy in Yemen received a threat about a potential attack on its compound, an American official said Monday, triggering heightened security measures in the capital, San'a. US Embassy spokesman Ryan Gliha told The Associated Press that the embassy was urging American citizens to exercise caution in Yemen. He said the embassy received a threat "regarding a possible attack that could take place in the foreseeable future" but gave no further details. In September, gunmen and two vehicles packed with explosives attacked the US Embassy in San'a. Seventeen people were killed during the attack, including six militants. Al-Qaida later claimed responsibility. A Yemeni security official said the US Embassy received a telephone call and an e-mail early Monday saying the US and Russian embassies in Yemen would be targeted by al-Qaida within a few hours.