Afghan President Hamid Karzai is set to begin a two-day visit to the US, where he will hold security talks with US President George W Bush.

But the trip is likely to be overshadowed by the detention in Afghanistan of 21 South Koreans by Taleban militants.

The Taleban have said they will meet a South Korean delegation, but have not yet agreed on a venue.

The US says the kidnapping shows the Taleban turning to terrorist tactics.

Some of the hostages - mostly young women - are reported to be ill.

The governor of Ghazni province, where the hostages are being held, says Pakistani Taleban and military intelligence officers have taken charge of the hostage situation from local Afghan Taleban, and are trying to show that the Afghan government is weak.

Four Afghans and a German are also being held hostage by another group of Taleban.

Iran worries

Mr Karzai will hold informal talks with Mr Bush at Camp David on Sunday.

He is expected to express concern that too many Afghan civilians have become the victims of coalition operations.

He also wants the US to press its ally, Pakistan, to do more to tackle fighters crossing the border into Afghanistan.

But the BBC's Jonathan Beale in Washington says the US is just as worried about the influence of neighboring Iran, accusing Tehran of supplying weapons to the Taleban.

Mr Bush is also expected to urge Mr Karzai to assert his government's authority throughout the country and root out corruption.

This year the US is giving Afghanistan $10bn, targeted at building up the country's own security forces.

Mr Bush wants to see results, correspondent says.

PHOTO CAPTION

Afghan President Hamid Karzai is and US President George W Bush – photo September 2006