Reports of explosions and gunfire at the DusitD2 hotel and offices in Nairobi’s Westlands district surfaced at around 3pm local time (midday GMT).
Eyewitnesses reported seeing four armed men, believed to be militants, throw bombs at vehicles before entering the hotel lobby, the BBC reports.
Images and footage from the scene shows hundreds of people fleeing the complex as gunshots ring out. The hotel says it is closed until further notice.
According to police sources, 15 people were killed, although the Kenyan government is yet to confirm the official toll.
The Foreign Office has confirmed a British-South African dual national was killed in the attack, and another Briton wounded. The US State Department confirmed a US citizen was killed.
An FCO spokesperson said: “We are supporting the family of a British man killed in the recent terrorist attack in Kenya. We are also supporting a British person who was wounded during the attack and is receiving medical attention. We stand ready to help any other British people affected.”
The FCO quickly updated its travel advice following the incident urging any Britons in the area to “remain vigilant” and follow the advice of local authorities.
“There is an ongoing security incident in the Riverside area of Nairobi; Kenyan authorities are conducting an operation in response to the incident,” said the FCO.
“If you’re caught up in the incident, turn any mobile phones or other devices to silent and do not put your location on social media. If you’re able to do so safely, leave the area and contact your friends and family to let them know you are safe.
“Remain vigilant and follow the advice and instructions of local authorities. The British High Commission Nairobi will be closed for routine business on Wednesday January 16 while we respond to the incident.”
Anyone directly affected can contact the British High Commission on +254 (0)20 287 3000. Anyone on the UK worried about a British national in Kenya can call the FCO in London on 020 7008 1500.
Somalia-based militant group al-Shabab has claimed responsibility for the attack.
