Kabul, April 7 (IANS): At least four policemen were killed and three others injured Monday when their van was struck by a bomb in Afghanistan, a police source said.

"A police van set off an improvised explosive device (IED) in Shindand district of Herat province at midday. As a result of the blast, four Afghan National Police members were killed and three injured," a provincial police spokesman Abdul Rauf Ahmadi told Xinhua.

The injured were shifted to a district hospital where they were in stable condition.

The Taliban home-made IEDs remained a major threat to Afghan security forces as the US and NATO-led troops in Afghanistan switched from combat to support role, namely training, advising and assisting Afghan forces.

Earlier Monday, a family member of a police official was killed in southern Uruzgan province.

More than seven million Afghans, of the 12 million eligible voters, Saturday cast their votes to elect a successor for outgoing President Hamid Karzai for the next five years in the first democratic transfer of power through polling in the country's history.