By Malcolm Haslett BBC Eurasia analyst

Khost province lies on Afghanistan's mountainous border with Pakistan.

Its valleys are relatively fertile, with important agricultural potential.

But it is the geographical situation which has given Khost a central role in the various rounds of fighting that have plagued the country for over 20 years.

It was a major base in the war between Communists and Islamic forces in the 1980s, with the Soviet army trying to cut off supply routes from nearby Pakistan.

The Pakistani city of Miram-Shah, just across the border, was used by mujahideen groups as a major supply base for their forces inside Afghanistan.

Strategic importance

Later, Khost became an important trading and logistics centre for the Taleban, linking their territory with Pakistan.

There is still support for the Taleban in Khost

It was headquarters for the Taleban's powerful Minister for Frontiers, Jalaluddin Haqani, and a sizeable number of the Taleban's foreign supporters were billeted in the town.

This is strongly Pashtun territory, and though many of its inhabitants are traditionally supporters of the king, there is no doubt there is also some residual support for the Taleban.

The situation in Khost is further complicated by rivalries between local leaders, vying for political control of the city and province.

None of this is helping the Karzai government and its international supporters to establish control of this vital border region.