The Taliban have begun operating in the key province of Kapisa, some 30km from the capital Kabul, Colonel Jonathan Ives told reporters here, speaking from Afghanistan in a telephone conference.

"We thought that it was safe and secure in this province, and so we considered it to be a non-threat area. And so we didn't apply or maintain a security force," he said.

"It's strategically placed in order to create access or provide them access to areas of significant influence," he said, adding that the fighters in question were particularly concentrated in one district, Tagab.

"They have grown specifically in this one area," he said. Taliban forces composed of members of the local Pashtun ethnic group have multiplied four-fold from about 50 to 200 fighters.

Ives is in charge of operations of coalition forces in the northeast of the country, as commander of the Cincinnatus task force.

Meanwhile, Afghan and foreign troops killed four men in anti-Taliban raids in eastern Afghanistan yesterday, police said as a local insisted the dead were villagers with no links to the rebels.

The US-led coalition said Taliban forces had opened fire on troops during the early-morning operations in the eastern province of Nangarhar and the soldiers had returned fire, killing some of them. It did not say how many.