(Adds U.S. soldiers' deaths, confirmation of shooting incident)

By Missy Ryan

BAGHDAD, Nov 18 (Reuters) - At least 17 Iraqis were killed by explosions in Baghdad and other Iraqi cities on Sunday, and three U.S. soldiers died in a suicide attack, Iraqi and U.S. officials said.

In Baghdad, nine people were killed and at least 20 others were wounded in one of the worst attacks in the Iraqi capital in several weeks, which police said targeted Iraqi Finance Ministry adviser Salman al-Mugotar.

A Finance Ministry source said Mugotar was unhurt in the blast in al-Hurriya Square in Baghdad's Karrada district, but at least two wounded were reported to be his security guards.

Brigadier-General Abdul-Karim Khalaf, a spokesman for the Interior Ministry, said the car that was targeted belonged to Satar Jabar, chief editor of the New al-Bayna newspaper, who was in the car but was reported to be unharmed.

A Reuters witness at the scene saw two burned corpses in the back of a police truck.

The U.S. military said three U.S. soldiers were killed in a suicide attack in Baquba, an ethnically mixed city 65 km (40 miles) north of Baghdad in the restive Diyala province.

It was not immediately clear if it was the same incident in which police reported that a roadside bomb in Baquba, targeting a U.S. foot patrol, killed at least three children, two of them siblings, and wounded seven people.

The attacks came as U.S. military spokesman Rear Admiral Gregory Smith heralded a 55-percent reduction in attacks since a deployment of an extra 30,000 U.S. troops was completed in June. Attacks are now at their lowest level since January 2006.

The drop in violence has also been attributed to improving Iraqi security forces and the growing use of U.S.-backed local police units organised by mainly Sunni Arab tribal sheikhs.

But U.S. and Iraqi officials say insurgency and sectarian strife between majority Shi'ites and minority Sunni Arabs, in which tens of thousands of Iraqis have died, could reignite.

CONVOY INVOLVED

A U.S. convoy was involved in the killing of two Iraqis on Sunday in what could be the latest in a series of incidents involving the U.S. military and Iraqi civilians.

A statement from the U.S. military and embassy in Baghdad said that initial reports indicated "an incident involving a U.S. military convoy resulted in the death of two Iraqi citizens and wounded four others". It did not give additional details.

"The coalition forces will work closely with the families, tribal and government leaders in Muthanna to convey our deep regret and ensure the families of those killed, and those who were injured, are properly cared for," the statement said.

The governor of the southern Shi'ite province of Muthanna had earlier accused U.S. troops of opening fire on civilian cars near Rumaitha, north of the provincial capital Samawa, 270 km (170 miles) south of Baghdad.

Governor Ahmed Marzok described the attack as "barbaric, brutal and illegal" and called for provincial officials to suspend cooperation with multi-national forces in the province.

Also on Sunday, a parked car bomb targeting a police patrol killed three people, including a woman in Mosul, 390 km (240 miles) north of Baghdad, police said. Four policemen were among 16 wounded.

Police said a roadside bomb killed an Iraqi army officer and a soldier and wounded another while they were trying to defuse the bomb in Tikrit, 175 km (110 miles) north of Baghdad.

In Baghdad, roadside bombs wounded two people in the Ameen district of southeastern Baghdad, and wounded another two in the Kesra neighbourhood of northern Baghdad. (Additional reporting by Waleed Ibrahim, Wisam Mohammed, Mariam Karouny; Writing by Missy Ryan; editing by Elizabeth Piper)

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