KABUL, Afghanistan --Hotel guest Abdul Zahir Faizada watched as a uniformed gunman shoved a man to the ground and shot him to death at point-blank range. Suddenly, gunfire erupted and another assailant blew himself up. By the time the siege of the luxury Inter-Continental Hotel ended Wednesday, 20 people lay dead -- including nine attackers, all of whom wore suicide-bomber vests -- and one of Kabul's premier landmarks was left a grisly scene of bodies, shrapnel and shattered glass. It was one of the biggest and most complex attacks ever orchestrated in the Afghan capital and appeared designed to show that the insurgents are capable of striking even in the center of power at a time when U.S. officials are speaking of progress in the nearly 10-year war. The brazen attack by militants with explosives, anti-aircraft weapons, guns and grenade launchers dampened hopes that a peace settlement can be reached with the Taliban and raised doubt that Afghan security forces are ready to take the lead from foreign forces in the nearly decade-long war. Faizada, the leader of the local council in Herat province who was in Kabul to attend a conference on that very issue, had just finished dinner at the hotel restaurant and was walking to his room on the second floor around 10 p.m. Tuesday when the militants struck. He said he saw five or six people in security-type uniforms clashing with the hotel staff and guards. "Suddenly I saw this guy in a uniform pushing a man to the ground. He shot him dead," Faizada said. For the rest of the night, Faizada and the mayor of Herat stayed locked in their darkened hotel room, whispering into cell phones with friends back in Herat who were giving them news updates of what was happening during the standoff. The attack came just a week after President Barack Obama said he would start withdrawing U.S. troops from Afghanistan next month. The suicide bombers struck on the eve of a two-day conference on transferring the responsibility for security across the nation to Afghan forces between now and the end of 2014. The U.S.-led military coalition, Afghan government and Ashraf Ghani, chairman of the transition commission, all vowed that the Afghan army and police would be ready in time. "Such incidents will not stop us for transitioning security of our country," Afghan President Hamid Karzai said. U.N. Secretary-General Ban Ki-moon said in a report circulated Wednesday in the Security Council that he was worried about attacks on civilians as the transition to greater Afghan leadership begins. "Persistent insecurity has brought about a steady rise in civilian casualties," he wrote, especially women and children "indiscriminately affected by the conflict." A man named Jawid, who was staying at the hotel when the attack occurred, isn't convinced the Afghan forces will ever be ready. "Where is the security in this country?" asked Jawid, who uses only one name. "Where is the security in this hotel?" Jawid escaped by jumping out the window of his room on the first floor of the Inter-Continental, which sits on a hilltop overlooking the capital. When the siege was over just after dawn Wednesday, 11 civilians were dead, including a judge from Logar province's court of appeals, five hotel workers and three Afghan policemen, according to Afghan intelligence officials. The Interior Ministry said a Spanish citizen was among the dead. The ministry said 18 people were wounded in the attack -- 13 civilians and five policemen. The State Department said three private U.S. citizens were at the hotel when it was attacked. Consular officers from the embassy were in touch directly with two of them who were unharmed and with the family of the third who "is getting medical care," spokesman Mark Toner said in Washington. The extent of the injuries to the third American were not clear, he said. An Afghan government official who toured the six-story hotel after the siege gave this account of the assault: The attackers entered the hotel compound from an area behind the kitchen and ballroom, which is in a separate building connected by a corridor to the main hotel. They moved down a hill covered with heavy vegetation to the front of the ballroom, where they killed two hotel guards. One attacker was slain. Some of the attackers took the corridor into the main hotel building where at least four climbed stairs to the roof to exchange fire with Afghan security forces, the official said. Other attackers went to the second and third floors and started knocking on hotel room doors, but the guests had been warned to stay locked in their rooms. Since authorities had cut off power to the hotel, militants used heavy flashlights to find their way. Night-vision goggles gave Afghan security forces the advantage as they hunted down the militants. Three suicide bombers died on the roof -- either by detonating their explosives-laden vests or from missiles fired by NATO helicopters that were called in to assist the Afghan forces. Two others blew themselves up on the second and fifth floors, the official said. "I was not able to even look into a room where they exploded themselves. The whole room was full of their body parts," said Matiullah, an Afghan policemen stationed at the hotel who suspects the militants slipped through 100-yard (100-meter) gaps between checkpoints surrounding the hotel. Four other attackers -- their bodies intact -- were found at different places in the hotel, including the rooftop. Latifullah Mashal, the spokesman for the Afghan intelligence service, said the Afghan security forces -- despite an assist from NATO advisers and three Black Hawk helicopters -- won the battle against the militants in the dark halls. "The enemy failed to carry out their plan," he said. "They were all killed and there was no major cost to civilian life. We are sorry for the loss of life, but we say to them: We Afghans have the ability to stop terrorist attacks, and we will." He suggested the attackers might have stored weapons in the area and then posed as hotel employees or workers at a construction site nearby. "So far, we don't know how they infiltrated," he said. "We do have a few clues." The Taliban claimed victory and boasted an inflated death toll: 50 foreigners, foreign and Afghan advisers and high-ranking officials. "One of our brave fighters carried out a suicide attack at the eastern entrance to the hotel and then we were all able to get in," Taliban spokesman Zabiullah Mujahid said in a statement recounting the operation. He said one fighter from Kunar province in eastern Afghanistan provided cellphone updates of the siege. "We are all inside the building and have already launched our attack with light and heavy weapons," Mujahid said the caller reported. "Until 4 a.m., they opened as many hotel rooms as they could, and when they were confident that foreigners were in the room, they opened fire and killed them. ... The resistance continued until 8 a.m." Afghan police were the first to respond to the attack, prompting firefights that resounded across the capital. A few hours later, an Afghan National Army commando unit arrived to help. Associated Press reporters at the scene heard shooting from rocket-propelled grenades, anti-aircraft weapons and machine guns through the morning. Flares and tracer rounds streaked across the sky. After hours of fighting, three NATO helicopters circled, clockwise, over the hotel -- with at least two firing missiles at the rooftop. U.S. Army Maj. Jason Waggoner, a spokesman for the coalition, said the helicopters killed three gunmen, and Afghan security forces clearing the hotel engaged the insurgents as they worked their way up to the roof. Missile fire from the helicopters and four loud explosions seemed to mark the end of the standoff. The lights in the hotel were turned back on. Ambulances started removing bodies from the scene. But later in the morning, Kabul Police Chief Gen. Mohammad Ayub Salangi said the last of the bombers, who had been injured and hiding in a room, blew himself up -- the finale to the deadly drama in the Afghan capital. The Inter-Continental -- known widely as the "Inter-Con" -- opened in the late 1960s, and was the nation's first international luxury hotel. It has at least 200 rooms and was once part of an international chain. When the Soviets invaded Afghanistan in 1979, however, the hotel was left to fend for itself. Attacks in Kabul have been relatively rare, although violence has increased since the May 2 killing of Osama bin Laden in a U.S. raid in Pakistan and the start of the Taliban's annual spring offensive. On June 18, insurgents wearing Afghan army uniforms stormed a police station near the presidential palace and opened fire on officers, killing nine. In late May, a suicide bomber wearing an Afghan police uniform infiltrated the main military hospital, killing six medical students. A month before that, a suicide attacker in an army uniform sneaked past security at the Defense Ministry, killing three people.