Three militants were killed and six others, including three policemen, sustained injuries in a clash in the southern Afghanistan province of Helmand on Wednesday, Afghan police said."A group of Taliban rebels raided a police checkpoint on a road in Tabili area early Wednesday morning and police returned fire, triggering a gun battle during which three armed insurgents were killed and six others, including three insurgents and three police, sustained injuries," Xinhua quoted Abdul Satar Norzai, a highway police officer in the province, as telling reporters.Taliban militants, have stepped up militancy after launching their annual so-called “spring offensive” on April 24.