At least 21 people - 13 foreigners and eight Afghans - were killed in an apparent Taliban suicide bomb and gun attack on a restaurant in a heavily fortified area of Kabul.

The assailants targeted Taverna du Liban, a Lebanese restaurant popular with expatriates and diplomats, in a neighbourhood of Kabul where many embassy buildings and offices of non-governmental organisations are located.

Ban Ki-moon, the UN secretary-general, strongly condemned Friday's attack through his spokesman, who said: "Such targeted attacks against civilians are completely unacceptable and are in flagrant breach of international humanitarian law."

Christine Lagarde, the chief of the International Monetary Fund, said Wabel Abdallah, 60, a Lebanese who had been the its representative in Afghanistan since June 2008, was among those killed in the attack.

A British citizen, a Russian, two Canadians and two Americans are known to be among the dead.

Zabiullah Mujahid, a Taliban spokesman, said his group carried out the attack.

"There was a suicide attack on a foreign hotel where special foreign invaders are coming for dinner," he said. "In this attack an explosive was used which was very strong and heavy casualties and massive destruction happened."

Heavily fortified area

The assault happened in the heavily fortified Wazir Akbar Khan district where many wealthy Afghans also live.

A suicide bomber detonated his explosives at the front door, before two other attackers entered through the kitchen and opened fire.

Ahmad Fawad, a cook at the restaurant, said: "We escaped to the neighbour's house through the roof. There were around eight or nine of us, hiding ourselves there.

"We could hear the shooting. Two attackers were inside. All the guests who were eating dinner were killed including our manager and the other cook."

Gunfire continued for about 20 minutes after the initial explosion before the attackers were killed by security guards, local government sources said.

General Mohammad Zahir Zahir, Kabul's police chief, said the 16 people killed were all inside the Taverna du Liban.

Ayoub Salangai, Afghanistan's deputy interior minister, said on Twitter that the dead included four women.

Officials said at least four other people were wounded.

The Taverna du Liban is one of three Lebanese restaurants in Kabul.

It has steel doors and customers have to pass through security to get in, as is the case with many restaurants in the city.

Al Jazeera's Jane Ferguson, reporting from Kabul, said the attack was a significant "breach of security" given the location.

"The scenes inside the restaurant is quite incredible," she said. "Anybody inside seems unlikely to have escaped from the gunmen."

Friday's assault is the first one to target a civilian restaurant since the Lake Qargha attack by the Taliban in the summer of 2012.

A series of attacks in 2013 targeted foreign compounds, the Supreme Court, the airport and the presidential palace in Kabul.