U.N. Secretary General Ban Ki-moon said the Norwegian foreign minister, who was not hurt, was the target of the assault, which came as the Norwegian embassy was holding a meeting at the Serena Hotel. Two U.S. State Department officials said at least one American was among the dead. A Norwegian reporter also died.
It was the first direct assault on a hotel in Kabul since the fall of the Taliban in 2001. The assailants also appeared to concentrate on the hotel's gym and spa, where foreigners relax and work out. An American inside said she saw a dead body and pools of blood in the lobby.
The militants killed six people and wounded six, said Interior Ministry spokesman Zemeri Bashary. One of the attackers was shot to death and the Taliban spokesman said a second died in the suicide explosion. It was unclear whether the Norwegian journalist was counted among the six dead.
Zabiullah Mujahid, a Taliban spokesman, told The Associated Press that four militants with suicide vests attacked the hotel - one bomber who detonated his explosives and three militants who threw grenades and fired guns and then fled. The claim could not be verified but came very soon after the attack.
Norway's Foreign Minister Jonas Gahr Stoere, who was in the hotel basement with a Norwegian delegation at the time, said he was about to start a meeting when the explosions hit, and everyone was ordered to lie on the floor for about 10 minutes.
"I don't think anyone could experience this without feeling you are in a serious situation," Stoere said on the TV-2 television network.
"Our security guards undertook an armed evacuation, where we went from corner to corner in the cellar until we reached a safe area," he told Norwegian reporters.
The U.N. secretary-general said Stoere was the target but could not say why.
"They do not care whoever, whatever. This is really a serious crime against humanity," Ban told several reporters at U.N. headquarters in New York.
Norway in past years has been singled out at least twice among nations al Qaeda has said should be targeted because of its participation in the NATO-led coalition in Afghanistan and a previous deployment in Iraq. However, there have not been any recent threats that authorities took seriously.
The founder of the al Qaeda-linked Iraqi extremist group Ansar al-Islam, Kurdish leader Mullah Krekar, is a refugee in Norway but was declared a threat to national security in 2005 and ordered deported. He has not yet been expelled.
Stoere arrived in Kabul on Monday, and had been scheduled to meet top leaders and some of the 500 Norwegian peacekeepers stationed in Afghanistan.
Stian L. Solum, a photographer from the Norwegian photo agency Scanpix, said a Norwegian journalist from the Oslo newspaper Dagbladet and a Norwegian diplomatic staff member were wounded and the journalist later died.
"We feel great sorrow and powerlessness," Dagbladet managing editor Anne Aasheim said on the paper's Web site.
The paper identified the dead journalist as Carsten Thomassen, 39.
"There were two or three bombs, and there was complete chaos," Solum said on the state radio network NRK. "When I started to walk out (of the elevator) a bomb went off, a little way from me. There were shots fired by what I think was an ANA (Afghan National Army) soldier."
The 177-room Serena is a newly built hotel frequently used by foreign embassies for meetings, parties and dinners. The nicest hotel in the city, Westerners often stay or eat dinner there. Located in downtown Kabul, it is near the presidential palace though separated by fences, blast walls and checkpoints. It is also near several government ministries and a district police station.
On its Web site, the hotel claims it is an "oasis of luxury in a war-ravaged city."
Aftenposten journalist Tor Arne Andreassen told the Oslo paper's Internet edition that he heard a grenade explode.
"Out the window I could see shots being fired at the guardpost by the gate," Andreassen said. He said he saw a female hotel employee so badly wounded that he did not believe she could have survived.
"The plaster flew around our room and the whole building shook," Andreassen said.
In Washington, two State Department officials said that at least one American was among the dead. The identity of the victim was being withheld until family could be notified, the official said, speaking on condition of anonymity ahead of a formal announcment of the death.
More than 30 U.S. soldiers in a half dozen Humvees rushed to the hotel as part of a quick reaction force, and security personnel from the U.S. Embassy ran through the hotel searching for Americans.
Suzanne Griffin, a Seattle resident who works with the aid agency Save the Children, said she was in the gym's locker room when the attack started.
"Thank God I didn't get into the shower because then we heard gunfire, a lot of it. It was very close, close enough that plaster came off the ceiling," said Griffin, her voice shaking. "We all just sat on the floor and got as far as we could from any glass and huddled on the floor. We turned our phones on silent."
Griffin, 62, said hotel staff evacuated the women to another part of the hotel. "We had to step over a woman's dead body. She was one of the gym people," she said.
She contacted the U.S. Embassy, which told her to not open the door unless she heard an American voice. U.S. soldiers evacuated her.
"There was blood on the floor all the way to the kitchen. There was a lot of blood in the lobby. There were empty shell casings outside," she said.
Earlier, the officials said no U.S. government employees were believed to have been in the hotel when the attack occurred. They said several Americans who had been there had called the embassy in Kabul to say they had not been injured. But the officials could not say if any private U.S. citizens were unaccounted for.
White House press secretary Dana Perino said it unclear who was responsible for the attack.
"It underscores the reason we have to stay on the offense against the extremists in places like Kabul but also in other places around the world," she said.
She said U.S. and NATO forces were waging a strong stand. "But we're in for a long, hard fight. These are deliberate, patient people who will murder innocents, including our own people."
In 2003, a rocket exploded near the Intercontinental Hotel in Kabul, knocking some guests from their restaurant chairs and shattering windows across the lobby and in many bedrooms. No injuries were reported.