At least 80 bodies - many with gunshot wounds and bearing signs of torture - have been found in Iraq in the past 24 hours, officials have said.
Iraqi officials believe they may have found a mass grave near Baquba
Iraqi security officials said they had recovered at least 52 bodies scattered around the capital, Baghdad.
Separately, the US said Iraqi troops had found 28 bodies south of the city of Baquba in what may be a mass grave.
The Red Cross (ICRC) condemned what it called the deliberate and appalling use of violence against Iraqi civilians.
In a statement, the ICRC urged all parties in the conflict to do their utmost to protect the civilian population.
The call came as US President George W Bush and Iraqi Prime Minister Nouri Maliki were meeting in Jordan to discuss escalating rebel attacks and sectarian violence in Iraq.
In other developments:
- a Sunni religious leader and at least six of his bodyguards were shot dead in an ambush in the southern city of Basra
- a US soldier was killed in combat in Baghdad on Wednesday, the US military said
In Baghdad, the bullet-riddled bodies of at least 52 people were found in different parts of the city, Iraqi officials said. Many of the victims bore signs of torture.
At the same time, Iraqi forces had found 28 bodies in what they believed was a mass grave near Baquba, about 60km (45 miles) north-east of Baghdad.
"The bodies were later transported to an Iraqi police station in Baghdad," a US military statement said.
The grim discoveries come amid the rising sectarian violence in the capital and across much of the country.
On Thursday, the ICRC said daily car-bombs, the shootings, abductions and killings had made normal life in Iraq impossible.
The ICRC said it was deeply shocked by the attacks, which it said were characterised by an appalling lack of respect for human dignity by the warring sides.