Meanwhile Mohammad Kazim Allayar, the deputy governor of Ghazi province, said that an intelligence service employee had been killed after being invited into a house and then kidnapped.
Taliban members were suspected of subsequently beheading the man, Allayar said, adding that the owner of the house was now under police investigation.
Two policemen were also reported killed by another roadside bomb in southern Afghanistan on Monday.
Taliban threats
Removed from power in 2001, the Taliban have threatened to step up their campaign against Afghanistan's Western-backed government this year.
Taliban commanders have said thousands of suicide bombers are waiting for orders to strike across the country.
On Sunday at least a dozen Afghans were killed when bombs exploded in the centre of the eastern city of Khost.
The last few months have seen some of the heaviest fighting between Nato troops and the Taliban since the US-backed Northern Alliance captured Kabul in late 2001.