UN leader Ban Ki-moon on Saturday strongly condemned a suicide gun and bomb attack on a Kabul restaurant in which four UN staff were among at least 14 fatalities.
A UN statement said other dead from the attack claimed by the Taliban were from other international organizations.
"Such targeted attacks against civilians are completely unacceptable and are in flagrant breach of international humanitarian law," Ban was quoted as saying by a spokesman.
Ban condemned the attack "in the strongest terms," said deputy UN spokesman Farhan Haq.
Four of its civilian staff were dead, the UN said, giving no other details about the victims.
The International Monetary Fund has already said its representative in Afghanistan was killed in the attack on a restaurant popular with foreigners.
The United Nations is to take on a leading role in Afghanistan as international troops complete their withdrawal in 2014 and the country builds up to national elections.
It has already tightened security at its bases, and the attack will lead to a new review of staff safety, UN officials said.
The UN Security Council condemned the latest attack "in the strongest terms."
"The members of the Security Council expressed their deep sympathy and condolences to the families of the victims, and to the people and government of Afghanistan, as well as to those other countries whose nationals have been victims of this attack," it said in a statement.
The Security Council "reiterated their serious concern at the threats posed by the Taliban, al Qaeda and illegal armed groups to the local population, national security forces, and international military and international assistance efforts in Afghanistan."