U.S., Iraqi forces prepare Najaf assault
More than 50 Iraqis killed in clashes across country
Insurgency spreads from Mehdi Army to other groups.
Cleric Muqtada al-Sadr says he will fight till the end in Najaf.
Iraq's interim prime minister makes a surprise visit to Najaf.
BAGHDAD, Iraq (CNN) -- With U.S. and Iraqi forces preparing for a major assault in Najaf, radical Shiite cleric Muqtada al-Sadr urged his armed followers to keep up their battle even if he is seized or killed.
The potential showdown comes after nearly a week of Iraqi and U.S. troops fighting the Medhi Army, which is loyal to al-Sadr. The cleric has many supporters in Baghdad, particularly in the Sadr City neighborhood, and in southern Iraqi cities.
"Iraqi and U.S. forces are making final preparations as we get ready to finish this fight that the Muqtada militia started," Col. Anthony Haslam, commanding officer of the 11th Marine Expeditionary Unit, said in a statement.
In a statement Wednesday, al-Sadr was resolute about continuing the battle but thanked those people who he said worked to establish peace in the city.
Over the weekend, U.N. Secretary-General Kofi Annan said the the United Nations was "ready to extend its facilitating role to the current crisis." Al-Sadr had said Tuesday that he welcomed the help.
Still, the violence continued into Wednesday. Over a 24-hour period that ended in the morning, 57 Iraqis in other al-Sadr strongholds were killed in clashes.
Of those, 29 died in the Meisan province in southeastern Iraq, a Ministry of Health official said. Fourteen people were killed in Baghdad, and 10 died in Diwaniya province. Basra reported four deaths, according to the official, who added 323 Iraqis were wounded.
On Tuesday, U.S. forces used loudspeakers to urge militants to surrender and residents to evacuate battle zones in the south-central city, which has an estimated population of about a half-million.
Members of the Mehdi Army militia are holed up in the city's Imam Ali Shrine, one of the holiest sites in Shiite Islam, and in the Wadi al Salam cemetery.
U.S. forces are firing back at militia positions in the cemetery but have not stepped foot in the sacred mosque compound.
U.S. military sources said the military is considering sending Iraqi forces, rather than Americans, into the compound.
Bomb explodes at market
Six people were killed Wednesday morning in a market explosion in Diyala province north of Baghdad, an Iraqi Ministry of Health official said.
Eleven people were wounded in the town of Khan Bani Saad, about 19 miles (30 kilometers) northeast of Baghdad, the official said.
"No policemen or national guards were in al-Dijaj market," a police officer said. "The terrorists want to kill everyone."
Other developmentsOn the outskirts of Falluja, Marines on the ground took fire from suspected insurgents manning heavy weaponry, Marine Lt. Col. Thomas Johnson said Wednesday. The Marines called in air support. Jet fighters bombed what the officials said was a team of about eight suspected insurgents manning the weaponry. It is not known at this time if there were any casualties. Controversial politician Ahmed Chalabi is in Iraq to face an arrest warrant, a spokesman for his Iraqi National Congress group said Wednesday. Chalabi is "in very high spirits and ready to face anything," the spokesman said. The warrant charges the former exile leader with counterfeiting. Also Wednesday, Chalabi's daughter Tamara announced in Washington that her father has filed a lawsuit against the government of Jordan. (Full story)Iran's supreme leader Wednesday denounced U.S. actions in Najaf as a crime against humanity and urged the international community to stop the violence, according to Iran's official Islamic Republic News Agency. "In the name of liberal democracy, one of the worst crimes against humanity is taking place in Iraq, especially in the holy city of Najaf," Ayatollah Ali Khamenei reportedly said.The Islamic Republic News Agency also said Wednesday that four employees are missing in Iraq. Armed men took the employees away from the al-Mansour district of Baghdad, the agency said. But an official at the Iranian Embassy in Baghdad said that three of the agency's staffers were arrested by Iraqi police for unknown reasons. The news agency said one of missing men was an Iranian; the others are local employees. An official with a main Shiite political party was gunned down Wednesday as he headed to Baghdad, according to a spokesman for the the Supreme Council for Islamic Revolution in Iraq. Ali al-Khalisi died in the drive-by shooting in Mahmoudiya, south of Baghdad, according to spokesman Abu Sara. One of Najaf's most noted residents, Ayatollah Ali al-Sistani, is still in England undergoing medical tests. Al-Sistani, Iraq's most influential Shiite cleric, doesn't need heart surgery, a representative said Wednesday, but he does have heart irregularities.
CNN's Matthew Chance in Najaf, and Kevin Flower, Eden Pontz and John Vause contributed to this report.