ISLAMABAD -- The U.S. Embassy in Islamabad on Sunday warned its staff of a possible attack on Americans at a top hotel in Pakistan's capital as the city was already on high alert following a suicide bombing earlier in the week.The U.S. government is aware of information that “unknown individuals are possibly plotting to attack Americans at the Marriott Hotel in Islamabad sometime during the holidays," the embassy said in a security alert.The embassy directive came two days after a suicide bombing in a residential area of the capital killed a police officer and wounded ten others.Militants with the Pakistani Taliban, who are separate from but allied with Afghanistan's rulers, later claimed the attack.Attackers drove a dump truck up to the hotel's gates before detonating it, killing 63 people and wounding over 250 others."