A total of 21 people, including 13 foreigners, died in a Taliban suicide assault on a popular restaurant in Kabul, police said Saturday, as witnesses gave horrific accounts of the carnage.

Desperate customers tried to hide under tables as one attacker detonated his suicide vest at the fortified entrance to the Taverna du Liban and two other militants stormed inside and opened fire.

Among the dead were two British citizens, two Canadians, a senior International Monetary Fund (IMF) representative from Lebanon, and the restaurant's Lebanese owner, who reportedly died after he tried to fire back at the attackers.

A Danish member of the European police mission in Afghanistan also died in the massacre on Friday evening, as well as four United Nations' staff whose nationalities was not confirmed.

"We were in the kitchen, and suddenly we heard a big bang and everywhere was dark," Atiqullah, 27, an assistant chef, told AFP by telephone as he attended a funeral for three colleagues.

"We used a backdoor to go to the second floor. Our manager went downstairs to see what was happening. We heard some gunshots and later found out that he had been shot dead.

"Afterwards, the police took us back into the restaurant to identify victims. We identified three guards who were killed.

"There was blood everywhere, on tables, on chairs, apparently the attackers had shot people from a very close range."

Popular with both Afghans and expats

The Taverna has been a regular dining spot for foreign diplomats, aid workers and Afghan officials and businessmen for several years, and was busy with customers on Friday, the weekly holiday in Afghanistan.

Like many restaurants in Kabul, it ran strict security checks with diners patted down by armed guards and passing through at least two steel doors before gaining entry.

On Saturday morning, the Taverna's battered sign was still in place, hanging over the ruined remains of the entrance door. Several badly damaged cars also remained at the scene.

"Our latest figure is 21 killed, including 13 foreigners and eight Afghans," Kabul police chief Mohammad Zahir told AFP.

"Five women were among the dead and about five people were injured."

UN Secretary General Ban Ki-moon condemned the killings, saying that "such targeted attacks against civilians are completely unacceptable and are in flagrant breach of international humanitarian law".

The assault was quickly claimed by Taliban militants fighting against the Afghan government and US-led foreign forces in the country.

A militant spokesman said the attack was to avenge a US airstrike in Parwan province on Tuesday night that Afghan President Hamid Karzai said killed seven children and one woman.

"These invading forces have launched a brutal bombardment on civilians... and they have martyred and wounded 30 civilians. This was a revenge attack and we did it well, and we will continue to do so," Zabihullah Mujahid said in a statement.

The insurgents regularly make exaggerated and incorrect claims about death tolls after attacks.

After the blast, elite security commandos had rushed to seal off the small streets around the restaurant as sporadic gunfire erupted. All three attackers died in the attack.

"A man came inside shouting and he started shooting," kebab cook Abdul Majid told AFP while being treated for leg fractures at a nearby hospital.

"One of my colleagues was shot and fell down. I ran to the roof and threw myself to the neighbouring property."

Afghanistan's intelligence agency has said it foiled several plots in the capital involving truck bombs and suicide gunmen over the past year.

"I express my deepest sympathies to the victims and families of those wounded and killed in last night's brutal and senseless attack," said General Joseph Dunford, the US commander of NATO forces in Afghanistan.

"Once again the Taliban have demonstrated their complete disregard for human life and shown their intent for the future of Afghanistan."

NATO forces are withdrawing from Afghanistan after more than a decade of fighting the Taliban, but negotiations have stalled on a security accord that would allow some US and NATO troops to stay after 2014.

Afghanistan's fledgling security forces face a difficult year as insurgents attempt to disrupt elections on April 5 that will choose a successor to Karzai, and as NATO's combat mission winds down by December.