Baghdad police say they have found 83 bodies, some showing signs of torture, in various locations around the city in the past 36 hours.
Sectarian violence is continuing unabated in Iraq
The fresh killings came as the US said seven more US soldiers had died, and that troops had killed 13 insurgents.
The Iraqi army has cancelled all leave and put troops on alert ahead of the verdict expected on Sunday in the trial of former leader Saddam Hussein.
Defence lawyers have warned of violence if he is sentenced to death.
The discovery of 56 bodies between Thursday and Friday mornings is the biggest in 24 hours since the Muslim holy month of Ramadan ended.
Another 27 were found during Friday.
Correspondents say some were probably victims of sectarian attacks, while others could have been targeted by criminal gangs seeking ransoms.
The 56 dead were all men, estimated to be aged between 20 and 45, police Lt Mohammed Khayon told the Associated Press.
They were all dressed in civilian clothing and found with their hands and feet bound, Lt Khayon added, saying that none of the men had yet been identified.
In other developments:
- In the US, a website set up to make public Iraqi documents from the Saddam Hussein era has been closed following suggestions that it included information on how to build a basic atom bomb
- It has emerged that a US audit office in Iraq, which has brought to light several cases of large scale fraud and waste in reconstruction efforts, is to be closed in October 2007
- US intelligence chief John Negroponte has held talks in Baghdad with Iraqi Prime Minister Nouri Maliki - issues discussed included building up the Iraqi security forces, the PM's office said.
US casualty figures have continued to rise in Iraq, following the deaths of more than 100 troops in October in one of the US's bloodiest months in Iraq.
Three soldiers were killed on Thursday in Baghdad when their vehicle was hit by a roadside bomb.
The same day, three soldiers were killed in the western Anbar province and another died "due to non-combat causes", the US military said.
The US military said troops had killed 13 insurgents during a raid involving both air and ground forces in Mahmoudiya, 30km (20 miles) south of Baghdad.
It was carried out after intelligence suggested an al-Qaeda-linked suspect was hiding in a house, the military said in a statement.
Five people were killed inside the building, including a man wearing an explosive vest, and eight were killed as they fled the area, the statement said.
Explosives and hand grenades were found in a search of the area, the military added.
The developments come as the Bush administration prepares for mid-term elections next week, in which correspondents say public frustration with US policy in Iraq is threatening to cause Republican losses.
Two days before the election, the Iraqi High Tribunal, which has been trying Saddam for crimes against humanity, is expected to deliver its verdict.
Saddam Hussein and co-defendants are accused of ordering the deaths of 148 Shias in 1982 in the village of Dujail, following an assassination attempt on the former president.
With a surge in violence during Ramadan, October was the fourth deadliest month for US troops since the US-led invasion in 2003.
Recent days have seen a number of public disagreements between US and Iraqi officials about attempts to improve security.
Mr Maliki has faced pressure to deliver on security, and take tougher action against sectarian militias.
He has blamed the Americans for the deteriorating situation, criticising the quality of equipment and training given to the Iraqi government forces.