The early Friday morning attack amounted to the first major effort by US and Iraqi forces to reclaim parts of Iraq in advance of nationwide parliamentary elections scheduled for January.
US troops and one battalion each from the Iraqi army and national guard stormed the city before dawn on Friday after a previous arrangement, signed on 9 September, which allowed for US forces to enter the town and patrol peacefully, fell apart a week ago.
At least 90 bodies and nearly 200 wounded were brought to Samarra General Hospital, said Dr Khalid Ahmad. The hospital was running out of bandages, oxygen and other supplies, he said.
Residents cowered in their homes as tanks and warplanes pounded the city overnight. The sound of loud shelling mixed with the crackle of automatic gunfire continued into the morning.
At least three houses were flattened and dozens of cars charred, residents said.
"We are terrified by
the violent approach used by the Americans to subdue the city. My wife and children are scared to death and they have not been able to sleep since last night"
Iraqi civil servant
"We are terrified by the violent approach used by the Americans to subdue the city," said Mahmud Salah, a 33-year-old civil servant.
"My wife and children are scared to death and they have not been able to sleep since last night. I hope that the fighting ends as soon as possible."
Military officials said two US soldiers were injured.
Water and electricity services were cut off and troops ordered residents to stay off the streets as they moved from house to house in search of insurgents. A 7pm-to-7am curfew was announced through loud-hailers.
Explosions started to shake the city at 1800 GMT on Thursday, residents said.
Within hours, US troops marched into the heart of the city, with armoured vehicles rumbling down the streets and helicopter gunships roaring overhead.
Clashes in Samarra risk drawing
towns nearby into the fighting
This was followed by clashes that continued throughout the early morning.
The governor of Salahulddin province, where Samarra is located, had warned on Thursday that new fighting risked plunging surrounding towns and cities into violence.
"I have warned the Americans if there is any violence in Balad and Duluiya, it is because of what is happening in Samarra," said Governor Hamid Hamud al-Qaissy, referring to nearby towns.
Al-Qaissy had earlier said local Iraqi officials were close to reaching a deal with local leaders to allow Americans to return to Samarra.
"An agreement will be announced soon. A previous signed plan with the coalition will be ready to work again and I will tell you as soon as it is finished," al-Qaissy said.
"I have warned the Americans if there is any violence in Balad and Duluiya, it is because of what is happening in Samarra"
Hamid Hamud al-Qaissy,
But the US attacked before any new deal could be reached.
The Americans moved with the backing of the Iraqi interim government, whose deputy prime minister, Barham Salah, announced the intention to seize back cities and towns before November.
Peaceful efforts to end the confrontation between Iraqis and US forces in Samarra unravelled on 23 September when US troops sealed off the city, including a crucial bridge over the River Tigris.
The blockading of the city shattered a peace agreement reached between the sides that allowed US forces to return to the city on 9 September after a three-month absence from Samarra.
The failed peace deal had been viewed as taking Samarra away from the brink of a major US assault to reclaim it from anti-US Iraqi fighters who had turned the city into a no-go zone for the Americans.