KABUL, August 23, 2008 (AFP) - Six mine clearers were kidnapped four days ago in Afghanistan, one of the most mined countries in the world, their agency said Saturday, as a global anti-landmine group demanded their release.

The men were among 13 captured by unknown militants early Tuesday in the eastern province of Paktia, said the director of the Mine Detection and Dog Centre (MDC), which is a contractor for the United Nations.

'After about 24 hours, seven of them were released. The remaining six are still captive,' director Mohammad Shahab Hakimi said.

The incident comes amid concern about the safety of aid workers in Afghanistan after three Western women and their driver were shot dead near Kabul 10 days ago, taking to 24 the number of aid workers killed this year.

The abductors had not demanded ransom and it was unclear if they were Taliban or ordinary criminals, Hakimi said. The kidnappers had also taken a pick-up and an ambulance.

Afghan deminers regularly fall victim to violence in the war-wracked country carried out by criminals or insurgents linked to the hardline Islamic Taliban, who were removed from government in 2001.

Twenty-two employees of the MDC, which has 1,800 staff working across the country, have been killed since 2001, mainly in areas where the Taliban still have influence, Hakimi said.

'Their strategy is to stop aid workers. Deminers have a very good name among society so they do not kill them -- they just threaten them.'

The International Campaign to Ban Landmines demanded the release of the men and called for militants to halt attacks on mine clearers.

'Deminers put their lives at risk every day to ensure the safety of their communities. Attacking them is a cowardly act and an assault on the entire civilian population,' executive director Sylvie Brigot said in a statement.

Afghanistan, which has suffered three decades of war, has the world's largest demining programme employing 8,000 Afghans, the group said.

The United Nations said last month that two-thirds of the country had been cleared of mines but four million people still lived on land planted with the devices.

The number of people falling victim to the explosives had dropped to a record low of 24 in June compared to 80 in February, it said.