A 20-hour Taliban siege in the Afghan capital ended Wednesday when local and international forces killed the remaining militants who had fired on the U.S. Embassy and NATO headquarters.

Six militants on Tuesday took over a half-built building overlooking the two compounds, which they fired on with automatic rifles and rocket-propelled grenades. Three other militants, armed with suicide vests, attacked Afghan police targets elsewhere in Kabul.

NATO helicopters working alongside Afghan security forces finally cleared the building of the last insurgents Wednesday, ending the siege.

The assault is believed to be the longest sustained attack in Kabul since the start of the Afghan war and killed 11 Afghan civilians and three Afghan police officers. More than two dozen people were wounded, including six NATO troops.

The U.S. Embassy said none of its staff were wounded in the assault.

The Taliban claimed responsibility for the assault, but U.S. Ambassador Ryan Crocker blamed the Pakistan-based Haqqani network for the coordinated attack in the heart of Kabul. The Haqqani network has ties to both al-Qaida and the Taliban and has demonstrated an ability to launch sophisticated attacks in the past.

Ambassador Crocker downplayed the assault, saying the militants were only capable of what he called “harassment” by firing just a half dozen rocket-propelled grenades from 800 meters away at the embassy.

Afghan police officials said they believe the militants used burqas to bypass security checks to get close to the sensitive area housing the diplomatic compounds. They reported finding several of the traditional full-bodied coverings for women inside a vehicle packed with explosives at the scene of the final battle.

Afghan President Hamid Karzai condemned the attack and praised the effective response of the Afghan authorities. He said such actions will not stop the security transition in the country, but instead embolden the Afghan people's determination to take responsibility for their own country's affairs.

The assault came as NATO nations seek to transfer full security control to the Afghan military within the next few years. U.S. and NATO officials responded to the violence by saying it would not weaken their resolve to continue the transition through the end of 2014. Afghan security forces already have taken security control of several cities and provinces.