A gunman burst into Kabul's Intercontinental Hotel restaurant and killed at least 14 foreigners along with four Afghans on Saturday.
However, some media reports indicate the number of dead could be much higher.
An eyewitness said he was spared after saying he was an Afghan. "Where are the foreigners?" they shouted.
The interior minister said the recent decision to transfer security to a private company had been a mistake.
Some 160 people were rescued after Afghan troops fought throughout the night to regain control of the building.
Three attackers were also killed in the siege, officials said. Ten people, including four civilians, were injured.
Kabul police told the BBC that nine Ukrainians, one German, one Greek and one Kazakh citizen had been confirmed dead. Two have yet to be identified.
Afghan airline Kam Air says a number of its employees were killed and some are still missing.
The Taliban, which targeted the hotel in 2011, says it was behind the latest attack. A spokesman said in a statement quoted by AFP that the group had "killed tens of foreign invaders and their puppets".
The gunmen burst into the six-floor hotel at around 21:00 local time (16:30 GMT) on Saturday evening, as guests were enjoying dinner.
The eyewitness told the BBC he was having dinner with his son when the gunmen began firing into the air with small arms.
They killed a woman - believed to be a foreigner - and turned the gun on the eyewitness himself.
Hotel manager Ahmad Haris Nayab said the gunmen had entered the hotel through a kitchen.
The Intercontinental is a state-owned hotel - not linked to the global hotel chain of the same name - which often hosts weddings, conferences and political gatherings.