Police say there has been a grenade attack on a disco in the Kenyan capital city of Nairobi.
At least fourteen people were wounded, Reuters Africa cited local media as saying.
The report came just hours after 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 Shabaab 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 statement did not specify who might carry out such attacks.
Last week, Kenya sent troops across its border with Somalia to hunt Shabaab 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 warplanes targeted the Shabaab-held Somali port city of Kismayo on Sunday as troops advanced on the insurgents and the US warned of an imminent threat of attack on foreigners in Kenya.
Nairobi sent soldiers across the border a week ago to hunt the al Qaeda-linked Shabaab fighters it blames for the abductions on its soil of a British tourist, a disabled French woman and two Spanish aid workers.
"The aircrafts targeted Shabaab positions including a military base and the seaport but we don't know if there were any casualties," said resident Abdikarim Maolim.
"Residents are shocked and the city is tense," he added.
Ahmed Yasin, another witness said: "I saw the two planes flying at low level but high speed and after five minutes they dropped heavy bombs that rocked the city."
Shabaab official Sheik Abddala Abu-Hassan said by phone that the raids had caused civilian victims but left their fighters unhurt.
Kenya has not said how many of its troops are deployed, but analysts estimate the number at between 2000 and 3000.
The troops are advancing in a three-pronged movement towards the Shabaab-held port city of Kismayo but their advance has been slowed by bad weather.
The radical Islamist Shabaab, who deny kidnapping foreigners, have repeatedly warned of bloody retaliation.
The latest threats came on Saturday from the Shabaab's leader Mohamed Abdi Godane:
"The Islamic regions in Somalia are all on high alert to prepare for the open war that is our response to the incursions by some neighbouring countries who are taking part in the global Christian invasion against Somalia," he said.
In response to the warnings, officials have beefed up security in Nairobi's central business district.
On Saturday security personnel moved bystanders further away from the entrance to the Hilton hotel and conducted identity checks on people who looked as if they could be Somali.
Kenya has a large Somali population, made up both of Somali nationals, many of whom have fled war and famine back home, and of ethnic Somalis who are Kenyan citizens.
In 1998, 224 people were killed in truck bombings at the US embassies in Kenya and Tanzania.
