NAIROBI - Kenyan President Uhuru Kenyatta announced Wednesday the end of a security operation following a terror attack on a hotel and office complex in the country's capital, killing 14.

Kenyatta told a televised news conference that all the terrorists who have attacked the DusitD2 Hotel complex have been killed, ending the 18-hour-long terror attack.

The security teams have evacuated Kenyans and foreigners from the buildings during the operation.

"We are grieving as a country this morning and my heart and that of every Kenyan goes out to the innocent men and women violated by senseless violence," said Kenyatta.

The president vowed to enhance the fight against global terrorism, saying "terrorism will never defeat us."

A mortuary attendant, who declined to be named, said earlier in the day that 15 people were killed as security officers engaged the terrorists in a gunfight on one of the hotel floors.

He said most of those killed are Kenyans and two are foreigners, and the US State Department has confirmed that one of the victims was an American citizen.

On Tuesday, United Nations Secretary-General Antonio Guterres condemned the "terrorist attack."

UN General Assembly President Maria Fernanda Espinosa Garces also condemned the attack.

"There is no justification for using terror and violence against innocent people," she said through her spokeswoman Monica Grayley.

Palestinian President Mahmoud Abbas called on all nations to combat terrorism after hearing the news of the attack, saying he condemns terrorism in all forms and manifestations.

The attack began at 3:00 pm (1200 GMT) Tuesday, said security officers.

Joseph Boinnet, inspector general of National Police Service, said the terrorists began their onslaught by setting ablaze three vehicles at a bank parking lot before moving to the DusitD2 complex.

At the entrance of the hotel, the assailants carried out a suicide explosion, injuring several people, said Boinnet.

Witnesses said the gang arrived at the hotel entrance and alighted before one of them started to shoot aimlessly.

The gunshots alerted police guarding the Australian embassy, which is located close to the hotel. The officers rushed there and engaged the gunmen in a gunfight, deflating the car that the terrorists had.

The officers managed to drive the terrorists to the hotel's main entrance, where guards on duty escaped on foot from the shootout, said Shadrack Kirui, a witness.

It was at that point that one of the attackers lobbed a grenade at three cars parked at the main barrier, setting them on fire.

The terrorists then proceeded to the main hotel lobby where one of them detonated an explosive device he had on his body.

Somalia-based terrorist group al-Shabaab has claimed responsibility for the attack. The group has been targeting Kenya-Somalia border areas and killing innocent citizens since Kenyan soldiers entered Somalia in 2011 to secure the two countries' shared border.