The U.S. embassy in Nairobi, Kenya has warned that it has received “credible” evidence of a possible terror attack on prominent Kenyan government buildings and Nairobi area hotels.

“Timing of the attack is not known, however, the Embassy has reason to believe that the potential attack is in the last stages of planning,” the embassy stated, adding that it urged Americans living in or visiting Kenya “to remain aware of their surroundings and vigilant of their personal security.”

In 1998, more than 200 people died after an attack on the U.S. embassy in Nairobi by al-Qaeda operatives.

In recent months, the new terror threat on Kenya has come from al-Shabab militants who rule much of neighboring Somalia. Al-Shabab, which is linked to al-Qaeda, has vowed to attack Kenya in retaliation for Kenya sending hundreds of troops into Somalia last year following a series of kidnappings of foreigners as well as cross-border attacks.

The Capital FM newspaper of Kenya reported that al-Shahab has already carried out a series of attacks on Kenyan soil, including grenade attacks in Nairobi, Mombasa and parts of northern Kenya.