BAGHDAD – Suspected Shiite militiamen fired mortars at two military bases and shot at a Polish helicopter south of Baghdad during clashes Monday that killed as many as five Iraqi civilians and wounded 20, officials said.

The Polish Defense Ministry said two Polish soldiers suffered minor injuries.

The fighting in Diwaniyah, a mainly Shiite city about 80 miles south of Baghdad, began when fighters from the Mahdi Army militia fired four mortar rounds at the main U.S. and Polish base and nine rounds at a patrol base manned mainly by Iraqis and Polish troops, an Iraqi military official said.

U.S.-led forces fired back with six or seven artillery rounds, and both sides traded small-arms fire, the official said. A curfew has been imposed on four districts in the city known to be dominated by the Mahdi Army.

The official, who spoke on condition of anonymity because he wasn’t authorized to release the information, said three Iraqi civilians were killed and 21 wounded in the crossfire.

A local policeman, who also declined to be identified because of security concerns, said Mahdi Army fighters emerged from alleys after the mortar attack and swarmed the smaller base, which had been set up in a youth center, prompting clashes that lasted about 30 minutes. He also said U.S. attack helicopters had opened fire. The U.S. military said it was looking into the report.

The officer said five Iraqi civilians were killed and 27 wounded, while the Polish Defense Ministry put the casualty toll at four Iraqi civilians killed and 17 wounded. The conflicting casualty reports could not be reconciled.

Lt. Col. Wlodzimierz Glogowski, spokesman for the Polish force in Diwaniyah, said a Polish helicopter came under machine-gun fire and two Polish soldiers had been slightly wounded.

He said Polish and Iraqi troops at the patrol base had fired back at the militants, but the civilian casualties were from the mortar fire.

Shiite cleric Muqtada al-Sadr’s office blamed the Americans for the attacks, saying civilians were targeted by aircraft. It also demanded the Iraqi government step in and stop military operations in the area, according to a statement.

Also Monday, a priest from a Catholic church in Mosul said he gave out incorrect information that two kidnapped priests had been freed. The Rev. Shamoun Matti said he was initially told by relatives of the priests that they were to be freed Sunday, and that he had mistakenly assumed the release had occurred.

A second official at the church, who asked not to be identified because he was not authorized to speak to the media, said the kidnappers had contacted the church at least three times Monday and were demanding $1 million ransom. “Negotiations with the kidnappers are still going on,” the official said.

Pope Benedict XVI appealed Sunday for the release of the priests who were ambushed, dragged out of their car and seized on their way home from a funeral. The pope asked the kidnappers to “let the two religious men go” during his traditional Sunday blessing in St. Peter’s Square.

In other violence Monday, an Iraqi journalist was killed in an ambush in northern Iraq, the second such attack in as many days.

Dhi Abdul-Razak al-Dibo, a 32-year-old freelance reporter, was attacked by gunmen as he was driving his BMW with two guards near Kirkuk, 180 miles north of Baghdad, Kirkuk police spokesman Brig. Gen. Sarhat Qadir said. The two guards were wounded.

Al-Dibo’s family said he lived in Kirkuk and contributed stories to at least two weekly newspapers in Tikrit, 80 miles north of Baghdad. The relatives, who spoke on condition of anonymity as they feared reprisals, said al-Dibo is survived by his wife.

The attack occurred a day after an Iraqi reporter for The Washington Post was shot to death in Baghdad.

Salih Saif Aldin, 32, an Iraqi who sometimes wrote under the name Salih Dehema for security reasons, was killed Sunday while reporting on the violence in the neighborhood of Sadiyah, the newspaper said.

Sadiyah is a formerly religiously mixed neighborhood in southwestern Baghdad.