The US embassy in Nairobi warned Americans of an "imminent threat" of attacks possibly targeting foreigners, one week after Kenyan forces crossed into Somalia to hunt down Shebab fighters.
The embassy cited "credible information of an imminent threat of terrorist attacks directed at prominent Kenyan facilities and areas where foreigners are known to congregate, such as malls and night clubs."
"The embassy has taken measures to limit official US government travel to Kenya and US citizens should take this information into account when planning travel and consider deferring travel at this time," the embassy added, in a statement provided by a State Department spokesman in Washington.
The statement did not specify who might carry out such attacks.
The State Department issued a travel warning for Kenya in December that remains current and warns of "continuing threats from terrorism and the high rate of violent crime."
Last week, Kenya sent troops across its border with Somalia to hunt Shebab insurgents it blames for the abductions of a British tourist, a disabled French woman who has since died in captivity and two Spanish aid workers.
Kenya has not said how many of its troops are deployed, but analysts estimate the number at between 2,000 and 3,000.
The Shebab, who deny kidnapping foreigners, have warned of bloody retaliation. In response to the warnings, officials have beefed up security in Nairobi's central business district.
In 1998, 224 people were killed in truck bombings at the US embassies in Kenya and Tanzania.