Two Turkish engineers kidnapped in Afghanistan last week have been freed after their employers apparently paid a ransom, police said on Monday.

Amid rising violence in the country, kidnapping has become a lucrative business and scores of locals and foreigners have been abducted by criminals or Taliban-linked militants in recent years.

The Turkish nationals were working on a project in the western town of Islam Qala, bordering Iran, when kidnapped last week. The pair were released last night, the police chief for the western zone said.

"Their company might have paid a ransom to the captors and bought their freedom," Ikramuddin Yawar told Reuters.

"Paying ransom to release people further encourages kidnapping in the country," he said, adding the abductors were part of a group of former factional forces who abandoned support for the government two years ago.

Islam Qala is on the main border crossing with Iran, a place where there is little Taliban activity. Criminals, however, have carried out kidnappings in the past and handed over their captives to the Taliban in return for money.

Two French aid workers were abducted in recent days in central Afghanistan, prompting their organisation, Action Against Hunger, to suspend activities in protest.

Nobody has claimed responsibility for their kidnapping.

Ousted from power in 2001, Taliban insurgents have been behind a number of kidnappings in Afghanistan. Some hostages have been killed, but most of the victims have been released unharmed.

The insurgents kidnapped 23 South Koreans last year, killing two and releasing the rest over a month later.