The U.S. embassy in Kenya warned of a threat to American citizens in the country after Nairobi launched a cross-border operation against Islamist militants in Somalia.
The embassy in a note to U.S. citizens living in or visiting Kenya said on Saturday that reprisal attacks could be directed at "prominent Kenyan facilities and areas where foreigners are known to congregate, such as malls and night clubs."
The statement said the embassy had taken measures to limit official U.S. government travel to Kenya.
Kenya launched its boldest incursion yet into its anarchic neighbor six days ago after a wave of kidnappings against foreigners that Nairobi has blamed on the al Qaida-linked al Shabaab militants. Al-Shabaab carried out attacks in July in Uganda which killed 76 people.
The rebels have denied responsibility for the kidnappings and said Nairobi was using them as a pretext for an attack.
The rebels have warned Nairobi to withdraw from its southern strongholds or risk bringing the "flames of war" into Kenya.
Reuters and The Associated Press contributed to this report.