The governor was a key figure in the Badr Organization, the military wing of the largest Shia Muslim party, the Supreme Islamic Iraqi Council (SIIC).

Khalil Jalil Hamza and police chief Maj-Gen Khaled Hassan were returning to Diwaniya city after a funeral when a bomb exploded beside their convoy.

The area has seen clashes between Shia militias and security forces.

It is believed to be the first time since the US-led invasion four years ago that the two most important officials of any province in Iraq have been assassinated.

Iraqi state television said the deputy governor had ordered an indefinite curfew in the province from 19:00 (15:00 GMT) in response to the killings.