The White House says Wednesday's deadly attack on a U.N. guest house in the Afghan capital is an attempt by extremists to disrupt the Nov. 7 runoff presidential election.

Press secretary Robert Gibbs said Wednesday the Obama administration believes attempts to interfere with the vote will not succeed. He also said the Afghan people will decide who their next leader will be.

SLIDESHOW: Deadly Taliban Attack in Kabul

Taliban militants wearing suicide vests and police uniforms stormed a guest house used by U.N. staff in the heart of the Afghan capital Wednesday, killing 11 people including five U.N. workers.

The two-hour attack, which began shortly before 6 a.m., sent people jumping out of windows or hopping from roof to roof to escape a fire that engulfed part of the three-story building. A man from Kansas City, Missouri, said he held off gunmen with a Kalashnikov until a group of guests escaped through the laundry room.

It was the biggest in a series of attacks intended to undermine next month's presidential runoff election. At least 25 U.N. staff were staying at the guest house, most of them advisers for the Nov. 7 balloting.

A Taliban spokesman claimed responsibility for the assaults, which included rocket attacks at the presidential palace and the city's main luxury hotel. The Taliban has warned Afghans to stay away from the polls or risk attacks.

The chief of the United Nations' mission in Afghanistan, Kai Eide, said the attack "will not deter the U.N. from continuing all its work" in the country.

"We will not be deterred from this noble mission," U.N. Secretary-General Ban Ki-moon said in New York.

One of the U.N. dead was an American, the U.S. Embassy said.

John Turner, a trucking contractor from Kansas City, said the attackers appeared well organized and were able to penetrate the building, located on a residential street.

Flushed and with black stains on his hands and face, Turner said 40 people were staying at the guest house, of whom about 25 took refuge in the laundry room at the back of the building under his protection.

"I am armed. I carry an AK-47 and I kept firing it to keep the attackers away from the group I was guarding," he said. The group later jumped over a back wall to take refuge in a house behind the guest house, he said.

"It is all plastic in there," he said, explaining how quickly the fire spread. "There was so much smoke, two women were completely overwhelmed."

Miles Robertson, an Australian working as an election adviser, said he and his wife fled to a closet in their bedroom when they heard gunfire.

"We made sure the door was locked. I actually put my wife in the cupboard to hide, and made the room look as if it wasn't occupied," Robertson said as he retrieved belongings from the burned-out guest house in the afternoon.

But then came the fire, which Robertson said appeared to be in the room next door.

"We realized that there was no way for us to go out under the stairs or any way for us to come outside," said Robertson, a lanky middle-aged man wearing a sweat shirt. "I opened the window and stepped out to the landing out front, and had a volley of shots fired at me."

So he ducked back into the bedroom, but it had filled with smoke. He worried about dying of smoke inhalation.

"I went to the bathroom, wet a towel and kept it over the face of my wife and myself as we crouched beside the window," he said.

Meanwhile, outside, "there was a lot of indistinguishable yelling and calling." Robertson said he made four phone calls to people saying they had about 10 minutes to get them out "because obviously the place was on fire."

He was too exhausted to finish the account, but a colleague said the Robertsons eventually climbed out a window as the fire raged and scrambled over the roofs of neighboring houses to a friend's home nearby.

A security guard, Noor Allah, said he saw a woman screaming for help in English from a second-story window and watched as terrified guests leapt from windows. Afghan police using ladders rescued at least one wounded foreigner.

Police were later seen pulling the charred body of what appeared to be a woman from a second-floor bedroom. One officer carried an injured German man by piggyback away from the scene.

About a mile (two kilometers) away from the guest house, one rocket struck the "outer limit" of the presidential palace but caused no casualties, presidential spokesman Humayun Hamidzada said. Two more rockets slammed into the grounds of the expensive Serena Hotel, favored by many foreigners.

One failed to explode but filled the hotel lobby with smoke, forcing guests and employees to flee to the basement, according to an Afghan witness who asked that his name not be used for security reasons.

President Hamid Karzai condemned the attack as "an inhuman act" and called on the army and police to strengthen security around all international institutions.

Taliban spokesman Zabiullah Mujahid claimed responsibility for the attacks in a telephone call to The Associated Press, saying three militants with suicide vests, grenades and machine guns carried out the guest house assault.

He said three days ago that the Taliban issued a statement threatening anyone working on the Nov. 7 runoff election between Karzai and Abdullah Abdullah.

"This is our first attack," he said.

An official with the U.N. election team said the Bakhtar guest house was home to the largest concentration of U.N. election workers in the city.

U.N. spokesman Adrian Edwards initially said six U.N. staff were killed and nine other U.N. employees were wounded. Later, he revised the figure to five, indicating one body may have been counted twice.

Afghan police and U.N. officials said 11 people in all were killed, including the U.N. staff, three attackers, two security guards and an Afghan civilian. It was not clear whether there were any other attackers besides the three killed.

The dead also included the brother-in-law of one of Afghanistan's most powerful governors, Gul Agha Sherzai. The man was killed by a stray bullet as he watched the gunfight from a nearby house, according to provincial spokesman Ahmad Zia Abdulzai.

Edwards said the U.N. would have to evaluate "what this means for our work in Afghanistan."

"This has clearly been a very serious incident for us," Edwards said. "We've not had an incident like this in the past."

The Aug. 19, 2003, truck bombing of the U.N. headquarters in Baghdad, which killed 22 people, prompted the U.N. to pull out of Iraq for several years.

Afghans are to vote Nov. 7 in a second-round election after U.N.-backed auditors threw out nearly a third of Karzai's votes from the Aug. 20 ballot, determining widespread fraud. That pushed Karzai's totals below the 50 percent threshold needed for a first-round victory in the 36-candidate field.

Dozens of people were killed in Taliban attacks during the August balloting, helping drive down turnout.