Suspected militants have attacked a luxury hotel complex in Nairobi, killing at least six people.

Gunfire and blasts were heard at the compound in the Westlands district of the Kenyan capital, which houses the DusitD2 hotel as well as offices.

The Somalia-based militant group al-Shabab said it was behind the attack.

Despite the government saying all the buildings were secured by Tuesday evening, fresh gunfire has since been heard.

Officials and witnesses said at least five people died at a restaurant in the complex in the incident, while another person died of their injuries in hospital.

A US citizen is among the dead, according to the US State Department.

But the total number killed is not yet confirmed - a mortuary worker told Reuters that it was at least 15.

The attack began at about 15:00 local time (12:00 GMT). The gunmen threw bombs at vehicles in the car park before entering the lobby, where one blew himself up, Kenyan police chief Joseph Boinnet told reporters.

A woman working in a neighbouring building told Reuters news agency: "I just started hearing gunshots, and then started seeing people running away raising their hands up and some were entering the bank to hide for their lives."

Police then rushed to the scene. One officer told the BBC's Ferdinand Omondi at the scene: "Things are not good. People are dying."

At 20:00 GMT, Interior Cabinet Secretary Fred Matiang'i said all the buildings in the complex had been secured by security forces.

"The situation is under control and the country is safe," he told reporters. "Terrorism will never defeat us."

An hour later though, gunfire was heard from the area.

Security forces were combing their way through the building hours after the attack started with reports saying frightened workers had barricaded themselves inside.

About 30 people are being treated at Nairobi hospitals, media reports say.

The five-star DusitD2 hotel has 101 rooms. Located in the Westlands suburb, minutes from the capital's business district, it has its own spa and several restaurants.

Kenya has seen a number of terror attacks in recent years - most notably in areas close to the Somali border and in the country's capital.