An Afghan policeman keeps watch at the scene of an explosion in Kabul January 17, 2014. [Photo/Agencies]

KABUL - Up to 15 people, mostly foreigners, were killed on Friday when a suicide bomber blew himself up outside a popular Lebanese restaurant in the Afghanistan capital of Kabul, police said.

Islamist Taliban insurgents claimed responsibility for the attack in the upscale Wazir Akbar Khan district, which hosts many embassies and restaurants catering for expatriates.

The International Monetary Fund (IMF) said its representative in Afghanistan was one of the dead, and the United Nations said three of its staff were killed as well.

"Such targeted attacks against civilians are completely unacceptable and are in flagrant breach of international humanitarian law," UN spokesman Farhan Haq said. "They must stop immediately."

General Ayoub Salangi, an Afghan deputy interior minister, said between 13 and 15 people, mostly foreigners, were killed but their nationalities were not immediately clear.

A Taliban spokesman said that those killed were German nationals. In Berlin, the Foreign Ministry said it could not confirm that Germans were involved.

The attack took place during a busy dinner time on a Friday evening when expatriates in Kabul tend to eat out. The heavily fortified diplomatic district also houses many wealthy Afghans and business people. Bursts of gunfire followed the attack.

"First there was a suicide attack near a restaurant for foreigners where a man detonated his explosives attached to his body, and then possibly one or two insurgents entered the restaurant," one Afghan security source said.

IMF representative Wabel Abdallah, a 60-year-old Lebanese national, was killed in the explosion, the IMF said. He had been leading the Fund's office in Kabul since 2008.

"This is tragic news, and we at the fund are all devastated," IMF Managing Director Christine Lagarde said in a statement. "Our hearts go out to Wabel's family and friends, as well as the other victims of this attack."

Interior Ministry spokesman Sediq Sediqi said three suicide bombers had approached the building, one of whom detonated his bomb whereas the other two were shot by security forces.