A Taliban assault on the Intercontinental Hotel in Afghanistan's capital killed at least 22 people, including 14 foreigners, and pinned security forces down for more than 13 hours before the last attacker was slain Sunday.

Authorities warned they were still investigating how militants breached security, which was taken over by a private company three weeks ago, at the landmark Intercontinental Hotel late Saturday.

Guests cowered behind pillars and in rooms as gunmen sprayed bullets and set fire to parts of the six-story building. Some people climbed over balconies, using bedsheets in a desperate attempt to escape.

The heavily guarded luxury hotel is popular among foreigners and Afghan officials.

Danish said 11 of the 14 foreigners killed were employees of KamAir, a private Afghan airline. KamAir also put out a statement saying some of their flights were disrupted because of the attack.

Six Ukrainians were killed in the attack on Kabul's Intercontinental Hotel, Ukrainian foreign minister Pavlo Klimkin said on Sunday.

"Reported to the President about the death of six Ukrainians as a result of an attack on a hotel in Kabul," he said on the ministry's Twitter account.

Ten other people, including six from the security forces, were reported wounded and more than 150 people, including 41 foreigners, were rescued from the hotel, Danish said.

A hotel employee told AFP that he saw two "fashionably dressed" gunmen in the hotel restaurant before the assault began.

"It was around 8.30 pm... They were sitting in the corner of the hotel, and they immediately started spraying bullets," the 20-year-old employee, who gave his name as Hasibullah, told AFP from his hospital bed.

He ran to a fifth floor room and locked himself inside, though not before seeing "many" bodies on the ground.

The gunmen went from door to door opening them "with daggers and shooting everyone". They were searching for foreigners, Hasibullah said, though Afghans were not spared. "They were saying kill the foreigners," he told AFP.

"We believe they were inside from before," he told AFP of the attackers.

On Sunday an interior ministry spokesman also suggested there was evidence some of the attackers had already been inside the building.

But it was too early to say if the militants had inside help, a second spokesman, Nasrat Rahimi told AFP, adding the investigation was ongoing.

The militants were armed with suicide vests, pistols, hand grenades and Kalashnikovs, he said.

The attack followed security warnings in recent days to avoid hotels and other locations frequented by foreigners in war-torn Kabul.

Security has been ramped up in the city, but the resurgent Taliban and Daesh are both scaling up their assaults.