In one of the biggest attacks, a car bomb exploded on Tuesday evening outside a Shia mosque in Baghdad's northeastern al-Hurriya neighbourhood, killing 21 people and injuring 43 according to a local security official.
The explosion came soon after three bombs went off in quick succession in Shia areas of the capital, leaving 30 people dead and 130 wounded.
Responding to the continuing violence, George Bush, the US president, said that Iraq must choose between "chaos and unity".
The blasts came as the trial of Saddam Hussein resumed after a two-week suspension of his trial.
Hours before Saddam returned to court, bombs wrecked the tomb of his father, Hussein al-Majid, in Tikrit.
High casualty rate
The new bloodshed came as a reminder of last week's violent reprisals between Sunnis and Shias after the bombing of a Shia shrine in Samarra.
The Iraqi government said that since the bombing in Samarra last Wednesday, 379 people had been killed and 458 wounded.
However, the Baghdad mortuary confirmed that it had received only 309 bodies since Wednesday, most of them victims of violence. Mortuary data showed this was double the average - it handled 10,080 bodies in 2005.
"The people of Iraq and their leaders must make a choice. The choice is chaos or unity"
In one of the attacks on Tuesday morning, a bomber blew himself up next to a queue of people waiting to buy kerosene in al-Amin in the southeast of Baghdad.
In the second attack, a car bomb exploded in the district of Jadida, according to an official from the Interior Ministry.
Six people were killed in another car bomb attack near a market in the central district of Karada.
Two British soldiers were killed in southern Iraq near the town of Amarra, according to the UK's Ministry of Defence.
Police also discovered nine bodies near the city of Baquba, the scene of several sectarian attacks since last Wednesday.
The coordinated attacks happened a day after the authorities lifted a daytime curfew and vehicle ban in Baghdad.
Activity was quieter than normal on the capital's streets with residents saying they were staying at home through fear of violence.
A US general described the
situation in Iraq as tenuous
In Washington, Bush expressed concern over the situation.
He said: "The people of Iraq and their leaders must make a choice. The choice is chaos or unity."
He declined to say how the unrest would affect US plans to lower troop levels this year.
The chief of US military intelligence, Lieutenant-General Michael Maples, sounded a bleak note, describing the situation in Iraq as "tenuous".
It was unclear whether the latest violence would strain efforts to lure Sunni parties back into talks on forming a new government after they left the negotiations last Thursday in anger over the attacks on their community.
Sunni participation in government is seen as crucial to ending the fighting, which has plunged Iraq into chaos since US forces overthrew Saddam's government in 2003.
The main Sunni political bloc, the National Concord Front, has indicated it will return to talks on a new government only if Sunni religious sanctuaries seized by Shia militias are returned to them.
Muwaffaq al-Rubai, Iraq's national security adviser, said 10 people, including four security guards, had been arrested in connection with the bombing of Samarra's gold-domed shrine.