Shouldering ammunition belts and rifles, newly U.S.-trained Afghan soldiers deployed by the hundreds to the western city of Herat (search) on Monday after some of the fiercest factional fighting since the fall of the Taliban (search) killed a Cabinet minister and as many as 100 others.

Forces loyal to Herat's governor, powerful warlord Ismail Khan, claimed to have retaken control of Herat by daylight Monday after tank, rocket and gun battles raged following Sunday's killing of Khan's son, Aviation Minister Mirwais Sadiq (search).

A militia commander, who admitted responsibility for the killing, was missing Monday, after Khan's forces retook the commander's division barracks and captured 150 of his men, Herat police chief Zia Mauddin Mahmud said.

Another 500 men loyal to militia commander Zaher Naib Zada surrendered, Mahmud said.

Zada, before his telephone fell silent around midnight Sunday, said between 50 to 100 people had died. Mahmud put the toll at 50 to 60.

The assassination and the fighting between Zada's and Khan's men rocked the shaky U.S.-allied government of President Hamid Karzai, still trying to assert control nationwide in a country rife with regional warlords after two decades of war.

Karzai ordered Afghan troops flown from Kabul to Herat after a late-night meeting with his security chiefs.

Six-hundred of the soldiers rolled out Monday at Kabul's airport, laden with bedrolls, ammunition belts, and rifles — one of the largest missions of Afghanistan (news - web sites)'s new army, and to calm internal fighting rather than confront outside enemies.

"We are going to keep the peace. We are not loyal to any side," Afghan Maj. Abdul Qadir said at Kabul's airport, as his fighters jogged out onto the airfield behind him.

The U.S. Embassy in Kabul on Monday urged all parties "to remain calm and abide by the rule of law and avoid further bloodshed."

"Afghanistan must not let the success of the last two years be put in jeopardy," the American statement said.

In Herat, shops were open, and people returned to the streets, said aid workers, who spent the night hunkered indoors, while U.N. workers had retreated to a bunker in their compound.

Two of the most powerful men of Karzai's government, Defense Minister Mohammed Fahim and Interior Minister Ali Ahmad Jalali, flew into Herat on Monday morning — sent to try to investigate and calm the situation.

The Cabinet ministers went first to pay condolences to Khan, who has gone all but unseen and unheard since the killing of his son. Mahmud said Khan was uninjured, but in mourning.

Circumstances of Sadiq's killing remained unclear. Presidential spokesman Khaleeq Ahmed said only that Sadiq had been shot Sunday in his car.

However, Zada told AP that his forces had killed Sadiq in a confrontation, after the minister went to Zada's home to fire him.

Afterward, Zada's forces and soldiers loyal to Sadiq opened fire with machine guns, tanks and rockets for control of his division's military barracks, he said.

Police, loyal to Khan, gave a different account from Zada's, saying Sadiq had gone to the residence to discuss a dispute.

The U.S. military at one point sent a B-1 bomber swooping over combatants "to help try to calm the fighting," U.S. military spokesman Lt. Col. Bryan Hilferty said in Kabul. He called the fighting an "internal" matter and said he knew of no American plans to intervene. The Herat post holds fewer than 100 personnel, including Americans, he said.

The U.S. Embassy in Kabul said Monday that German and Italian diplomats were sheltering at a U.S. base in Herat.

Karzai, who himself escaped a 2002 attempt on his life, said in a brief statement that he was "deeply shocked" by the killing and offered condolences to Ismail Khan.

Karzai's first civil aviation minister, Abdul Rahman, was assassinated Feb. 14, 2002, at Kabul's airport. Gunmen shot and killed Vice President Abdul Qadir in the capital on July 6, 2002.

Both of those killings remain unsolved.

Karzai's government includes an uneasy alliance of former warlords who joined forces to help the United States rout the former Taliban government. His government still is trying to establish authority nationwide, including over Herat, a major port of entry on the Iranian border, and its customs revenue.