Western and Afghan officials have admitted that Taleban militants breached the outer defences of a remote US base during a battle in Kunar province on Sunday that claimed the lives of nine US soldiers and wounded 19 coalition troops.

In the first detailed account of the assault on the US “combat outpost”, Nato confirmed yesterday that the insurgents had come close to wiping out the base, which was only three days old. It was “a pretty close run thing,” a military source said.

The attack, a frontal assault rarely attempted by the Taleban since they lost hundreds of fighters in similar raids on British outposts in Helmand in 2006, began 15 minutes after the first call to morning prayers at the local mosque.

The combat outpost was rudimentary, a ring of barricades and sandbags designed to shield the occupants from small arms and rocket-propelled grenades. Its defensive towers and fortifications were still under construction. On three sides it was overlooked by the village of Wanat, high in the restive Weygel Valley.

“It was a complex attack, well organised and planned ... it was clear they wanted to over-run the combat outpost,” said Captain Michael Finney, spokesman for Nato's International Security Assistance Force (ISAF).

The force of several hundred reportedly infiltrated the area and took up positions in houses, shops and the mosque overlooking the US base on Saturday night. Some reports spoke of a joint assault including members of the Taleban, al-Qaeda fighters from neighbouring Pakistan, Arabs and Chechen “foreign fighters” and members of Hizb-eIslami, an allied insurgent group.

They fired mortar bombs, rocket-propelled grenades and machinegun rounds from the surrounding buildings. The US forces, supported by a few local Afghan police, are believed to have numbered no more than 100. Western forces defending the base sustained their biggest losses in a single battle since 2001.

A military source said that the fighting was brief and that the situation began to stabilise as attack aircraft arrived. A Nato spokesman said that the Taleban lost “scores” of fighters. “There was very heavy fighting and they suffered very heavy casualties,” said Mark Laity.

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