Taliban gunmen and suicide bombers attacked Kabul's Hotel Inter-Continental in a carefully orchestrated attack that began Tuesday night and continued into Wednesday.
About four hours after the attack began, International Security Assistance Force helicopters fired at insurgents on the roof, killing as many as three of the gunmen, ISAF spokesman Maj. Tim James told CNN.
In addition, at least 20 Afghan forces had entered the hotel and were working their way up floor by floor, he said.
Two of the approximately six would-be suicide attackers whose attack on the hotel began at 10 p.m. Tuesday were shot dead by police; another detonated his explosives and two were still resisting from the top levels of the hotel, said Afghan Lt. Gen. Mohammad Ayoub Salangi, the city's chief of police, shortly before the ISAF spokesman told of the helicopter attack on the roof.
The Afghan National Police and the Afghan army were in control of the area, he told CNN, adding that the overall casualty toll was not clear.
The first and second floors of the hotel were cleared and police and army security forces were trying to clear the top three floors, Salangi said.
A spokesman for the Taliban, Zabiullah Mujahid, said in an e-mail that the suicide attackers entered the hotel after killing the security guards at the entrance.
"One of the suicide attackers told us on the phone that they are in the lobby and chasing guests into their rooms by smashing the doors of the rooms and he added that they have killed about 50 guests of this hotel," Mujahid told CNN in an e-mail.
Salangi could not confirm any casualties - but a U.S. official, speaking on condition of anonymity, said at least 10 people had been killed. There were no indications that U.S. military or diplomatic personnel were at the hotel, U.S. officials told CNN.
The Inter-Continental is popular among international guests. A news conference had been scheduled to take place there Wednesday to discuss the planned transition of security from international to Afghan forces that U.S. President Barack Obama announced last week. Obama was briefed on the attack while en route back to Washington from Iowa, White House spokesman Jay Carney told reporters.
Three Taliban fighters penetrated the hotel's typically heavy security in the attack, and one of them detonated an explosion on the second floor, said Erin Cunningham, a journalist for The Daily in Kabul.
"We're continuing to hear small-arms fire right now," she told CNN from a vantage about 500 meters (a third of a mile) from the hotel more than an hour after the attack. Several snipers were on the roof firing at Afghan security forces, she said.
A few minutes beforehand, she said, rocket-propelled grenades were launched from the roof of the hotel toward the area of the first vice president's house. A few moments later, she said the hotel was rocked by three explosions, one of which knocked her off her feet. U.S. forces were on the scene, she said.
Members of the Afghan National Security Forces were on the scene, but the city police had the lead, ISAF Maj. Jason Waggoner said in a statement. Waggoner said ISAF forces were providing "some limited assistance."
Electricity around the hotel was shut off, said Jerome Starkey, a reporter for The Times.
The hotel was developed by the InterContinental Hotels Group and opened in 1969. But it has had no association with the group since the Soviet invasion in 1979, though it continues to use the name and logo without connection to the parent company.
The incident came on the same day that Lt. Gen. William B. Caldwell announced that NATO and other members of the international community involved in Afghanistan have decided to increase the number of security forces in the Afghan National Army and the Afghan National Police to 352,000.
The current number of Afghan National Army and Afghan National Police is about 300,000, the commander of the NATO training mission in Afghanistan and commanding general of the Combined Security Transition Command told the Atlanta Press Club.
The increased number will be sufficient to give the Afghans security without coalition forces having to do it, he said.
CNN's Reza Sayah in Islamabad, Pakistan, Tom Watkins in Atlanta, Barbara Starr, Larry Shaughnessy and Elise Labott in Washington and journalist Jonathan Boone in Kabul contributed to this report.