The governor and police chief of Iraq's Shia province of Diwaniya were killed when a roadside bomb hit their convoy of vehicles on Saturday, police said.
Diwaniya governor Khalil Jalil Hamza and police chief Major-General Khaled Hassan were returning to the provincial capital of the same name, 180 km (110 miles) south of Baghdad, when their convoy of four-wheel drives was hit.
Hassan had been in the job for less than a week, police said. Hamza was a member of the Supreme Islamic Iraqi Council (SIIC), the biggest Shia party in Iraq.
They had been attending the funeral of a leading tribal sheikh in the town of Efaj, 30 km (18 miles) east of the city.
Three of their bodyguards were killed and three others wounded. Local authorities quickly imposed an indefinite curfew.
One policeman said the bomb was an "explosively formed penetrator", a particulaly deadly form of armour-piercing bomb which U.S. forces accuse Iran of supplying to Iraqi militias.
The SIIC's armed wing, the Badr Organisation, has been in conflict with the Mehdi Army militia of powerful anti-American Shi'ite cleric Moqtada al-Sadr.
The Shia-dominated south has become increasingly restless as factions vie for control of the oil-rich region, often pitting police loyal to one bloc against militiamen of others.
US forces have also been pursuing what they describe as rogue elements of Sadr's Mehdi Army, who are accused of bringing in weapons and receiving training from neighbouring Iran. There were heavy clashes in mid-April when US and Iraqi forces fought to wrest control of the city back from the Mehdi Army.
The second most senior US general in Iraq said Iran was supplying militias in Iraq with more weapons to attack US troops in a bid to influence debate on the war in Washington ahead of a crucial progresss report due in weeks.