Afghan police say a roadside bomb has killed 3 civilians in western Afghanistan.

Police spokesman Noor Nikzad says the Monday morning blast was in Herat city. He says the bomb was hidden in a sack in an irrigation ditch.

When officers went to inspect the object, it exploded. The three civilians who were killed were walking nearby and caught up in the blast. He said no police were killed, though one was wounded.

Meanwhile, NATO forces say that a detainee captured in an operation in the south was found dead in his holding cell Sunday.

NATO says the man was being held in Kandahar province after being detained Saturday, and the alliance is investigating the circumstances of his death.

The international military coalition gave no further information.