Uhuru Kenyatta said early on Wednesday that operations at the dusitD2 hotel in the centre of the Kenyan capital had ended and that 14 “innocent lives” had been lost.

More than 700 civilians had been safely evacuated, he said.

The attack on the began shortly after 3pm on Tuesday with an explosion in the parking lot and then a suicide bomb blast in the hotel’s foyer, police said.

The assault on a compound in the centre of the Kenyan capital containing restaurants, a spa and several office buildings housing international companies as well as the luxury hotel, was the most high-profile by terrorists in Kenya for many years.

The attack was claimed by al-Shabaab, the militant Islamist organisation based in neighbouring Somalia, on its in-house radio network and online. Al-Shabaab was responsible for an attack on Nairobi’s Westgate Mall in 2013 that left at least 67 people dead.

Kenyatta pledged to “pursue relentlessly those involved in the funding, planning and execution of a heinous act wherever they will be” and said the country was on “highest alert.”

Images from security cameras showed four young men in black combat fatigues and loaded belts, armed with AK47s entering the compound.

The gunmen initially targeting a bank and diners at a Thai restaurant, prompting panic.

Survivors reported hearing a shattering blast and saw people mown down by gunmen as they sat at a cafe. Victims were left lying on tables, bleeding.

“We were changing our shifts, and that is when I heard a loud blast and people were screaming,” said Enoch Kibet, who works as a cleaner at the cafe and managed to crawl out of a basement gate. “I couldn’t believe I was alive. The blast was so loud and shook the whole complex.”

In the hours after the attack, the gunmen and security forces engaged in a series of sporadic but fierce firefights. Plumes of smoke rose into the air from several burning cars. “There was a bomb, there is a lot of gunfire,” said one man working at the complex, who asked not to be named.

Others described office workers in the complex hiding under the desks or sheltering behind makeshift barricades. Injured casualties were still being brought out of the complex around 7am this morning, when gunfire and blasts were heard.

Western and international security officials have told the Guardian they warned Kenyan counterparts of high profile attacks by al-Shabaab, an affiliate of al-Qaida, over Christmas and the new year.

Tuesday’s attack came exactly three years after an al-Shabaab attack on a Kenyan military base in El Adde in Somalia, in which about 140 Kenyasoldiers were killed.

However experts say the organisation has other motivations for attacking Nairobi, a city it sees as a “Western bastion”.

Kenyatta said operations to “deter, disrupt and defeat” terrorist operatives and groups” were underway throughout Kenya.

“I assure every Kenyan and foreign visitors that you are safe in Kenya,” he said.

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