Taliban claims responsibility for strike in which two Britons, two Americans and two Canadians are among those killed

Two Britons and two Americans were among at least 21 people killed when a suicide bomber and gunmen attacked one of Kabul's most popular restaurants.

The head of the International Monetary Fund's Afghanistan office and three UN staff of the were also killed in the attack on Friday evening, along with the Lebanese restaurant owner, several Afghans, and two Canadians.

The Taliban claimed responsibility for the attack in the well protected district in Kabul where most foreign workers live and work.

A suicide bomber blew himself up at the entrance to the restaurant, killing guards and destroying defences and allowing two gunmen to enter and open fire.

The Foreign Office named one of the British victims as Dhamender Singh Phangurha, who is better known as Del Singh, a Labour candidate for the European elections. The other Briton has been named as Simon Chase from County Londonderry, who was the bodyguard of a Danish, female police officer who was also killed. A spokeswoman said she did not believe there were any other British injuries.

Kabul police chief Mohammad Zahir said the victims included 13 foreigners and eight Afghans; two Britons, two Canadians, a Malaysian, a Dane, a Russian, two Lebanese, a Somali-American and a Pakistani. At least four people were wounded, and about eight Afghans, mostly the kitchen staff, survived.

The Taliban claimed responsibility for the attack, saying it was in reprisal for an Afghan military operation earlier in the week against insurgents in eastern Parwan province, which they said killed many civilians.

"The target of the attack was a restaurant frequented by high-ranking foreigners," Taliban spokesman Zabihullah Mujahid said in an emailed statement. He said the attack targeted a place "where the invaders used to dine with booze and liquor in the plenty".

The Labour leader, Ed Miliband, paid tribute to Singh: "My thoughts – and the thoughts of the whole Labour party – are with the family and friends of Del Singh who was killed in yesterday's tragic suicide bomb in Kabul.

"People everywhere will be appalled and shocked by this barbarous act of terror deliberately targeting members of the international community living and working in Kabul in the service of the Afghan people.

"Del spent over 10 years carrying out vital work on development projects in Afghanistan, Kosovo, Sudan, Sierra Leone and other countries. He dedicated his life to working with people across the world who needed his support."

Labour MP Stella Creasy tweeted: "Shocked to hear of death of del Singh in Kabul – condolences to his family and friends."

William Morrison, managing director of Adam Smith International, Singh's employer, said: "Del was skilled at drawing people together – his presence made meetings flow more smoothly, and helped difficult negotiations reach amicable conclusions. His professionalism, reliability, and irrepressible good humour made him well-known throughout the budget department and the close international community in Kabul. Del was the sort of person who was always welcome in any room or any discussion – it was impossible to be bored or out-of-sorts when Del was around."

Singh's colleague, Malaysian adviser Gnana Nagarajah, was also killed. He was described as possessing a "razor-sharp mind, deep experience, and kind-heartedness". Morrison said: "It was impossible not to love him – for his generosity, which delighted in giving gifts to others and cooking elaborate meals for his friends; for his caring nature, which made him the sort of person who thought the best of everyone and always looked out for the welfare of others; and for his gregariousness, which led him to host parties and surround himself with friends.

"Gnana and Del had this in common: they were an unqualified pleasure to work with, to live with, and to spend time with. It was a profound privilege to have known and befriended them - their death is an enormous loss."

The Canadian foreign affairs minister, John Baird, said two Canadians died in the attack while the US state department said two Americans were killed. None of the four worked for their national governments or armies.

The restaurant's popular owner, Lebanese citizen Kamal Hamade, was among the dead. "VV sad news Kabul. Our dear Lebanese friend Kamal, the kindest of hosts, was killed in Taliban attack," BBC journalist Lyse Doucet said on Twitter.

The IMF said their country head, Lebanese citizen Wabel Abdallah, had worked in Afghanistan since 2008.

The attack will make life increasingly difficult for the foreign agencies, both private and governmental, which administer billions of pounds of aid and development projects in Afghanistan. Most international staff are subject to elaborate security arrangements and defences, which the Taliban have demonstrated can be neutralised when they want. It is possible they will decide that the risks are too great for foreign staff, and end or reduce their projects.

Afghanistan has a presidential election in April and foreign troops are scheduled to leave in 2014.

Friday's attack began with a bomb blast that shook the Wazir Akbar Khan neighbourhood shortly after 7pm, as one attacker detonated his explosives at the restaurant's front gate.

It was followed by more than two hours of sporadic gunfire, as Afghan commandos besieged two other attackers. One of the survivors, Suleiman, who worked as a cook at the restaurant, said he escaped from the gunmen after hearing the explosion outside.

"I went to the roof and stayed with my back to the chimney for two or three hours. Later Afghan police came and took me out," he said.

It was the deadliest day for the UN in Afghanistan in nearly three years. In April 2011 a rioting mob overran a compound in northern Mazar-e-Sharif city, killing three UN workers and four Nepalese security guards. Eighteen months earlier, in autumn 2009, five UN workers were killed in Kabul when gunmen burst into a guesthouse for the organisation's staff.

The deaths had a far-reaching impact on how the UN and many other international organisations worked in the Afghan capital.

Although there are regular attacks on targets in the Afghan capital, it is rare for attackers to make it through rings of security around the city, elude an extensive intelligence network, and strike at a civilian target around the unofficial "green zone" that houses Nato and US embassy headquarters.

A single suicide attacker killed an Afghan family, including a human rights chief, with a bomb at a nearby supermarket three years ago, but security has been tightened since then at most places frequented by the Afghan elite or foreigners.

Friday's target, the Taverna restaurant, was a popular venue usually busy on a Friday. It had armed guards and an air-lock entry system of steel gates, but those precautions would have been little match for a heavily armed suicide squad.