Prime Minister Nouri al-Maliki called Sunday for Iraqi Shiites and Sunnis to use the Islamic holy month of Ramadan to put aside their differences and end sectarian violence, a day after a retaliatory bombing killed dozens of Shiites in the capital.

A disagreement over the day Ramadan begins showed the depth of differences between the country's two major Muslim sects. Sunni Arabs began observing Ramadan on Saturday, while Iraq's most influential Shiite cleric, Grand Ayatollah Ali al-Sistani, declared the start of Ramadan to be Monday.

The bombing in the Shiite slum of Sadr City killed 38 and wounded 42 as they stocked up on fuel for Ramadan, days after the U.S. military warned that sectarian bloodshed could worsen during the holy month.

The group claiming responsibility said it carried out the bombing to avenge a Friday attack by a suspected Shiite death squad on Sunni Arab homes and mosques, which killed four people in a mixed Baghdad neighborhood.

In a statement, al-Maliki pleaded for unity.

"We are all invited to make use of these days to strengthen the bonds of brotherhood and avoid anything that could hurt the social fabric of the Iraqi people," al-Mailiki said. "Iraq is living in a very sensitive and historic period."

Al-Mailiki pleaded for support for his nascent government. An incident in Tikrit was a grisly reminder of the challenges it faces.

AP Television News footage from the city's morgue showed medics working to identify the severed heads of 10 Iraqi soldiers that were tossed into a crowded market in nearby Beiji by unidentified gunmen Saturday.

Nearby was the covered body of police Col. Ismaiel Chehayyan, killed by gunmen while breaking the Ramadan fast at a friend's house.

At least six people were killed in Baghdad when a car bomb exploded by a police patrol near the Health Ministry, which was shelled earlier in the morning in a mortar attack that wounded three.

The bomb attack killed four policemen and two civilians. Four officers were wounded, along with two civilians.

Another six people were killed and 25 were injured in scattered violence around Iraq:

— A car bomb targeting a police patrol in eastern Baghdad killed two people and wounded 13.

— An Iraqi soldier was gunned down in his car in east Baghdad on his way to report to his unit, police said.

— Two Iraqi soldiers were killed and another two were injured when a homicide car bomber slammed into a checkpoint in Tal Afar, 260 miles northwest of Baghdad. The soldiers opened fire on the car as it sped toward the checkpoint but were unable to prevent the detonation, police said.

— In Mosul, 225 miles northwest of Baghdad, a bomb blast wounded two civilians, police said.

— One person was killed and five others wounded when their house was hit with a mortar shell in the town of Al-Musayyab south of Baghdad in the Babil province, police said.

— Police said they found more apparent victims of sectarian death squads in eastern Baghdad, whose five bodies bore signs of torture and were blindfolded with their hands and legs bound.

Sunni extremist group Jamaat Jund al-Sahaba — or Soldiers of the Prophet's Companions — claimed responsibility for the Saturday bomb attack on Shiites in Sadr City, home to more than 2 million people and a stronghold of radical Shiite cleric Muqtada al-Sadr.

Police said the bomb went off as people crowded behind a kerosene truck to buy fuel for Ramadan, during which people gather just after sunset for a communal meal to break a daylong abstention from food and water.

Jamaat Jund al-Sahaba blamed al-Sadr's Mahdi Army militia for the Friday attack that killed four people in the Hurryah neighborhood, where a Shiite militia last week openly threatened members of the Sunni minority.

Meanwhile, an Internet statement posted Sunday said that the leader of an Al Qaeda-linked terror group had not been captured, contradicting an Iraqi government report.

Iraq's armed forces announced the arrest Friday of Muntasir Hamoud Ileiwi al-Jubouri, a senior leader of the Ansar al-Sunnah group, and two of his aides near Muqdadiyah, 55 miles northeast of Baghdad.

In another statement issued Sunday, the group said it had killed 10 Pakistani and Indian Shiite Muslims in the western province of Anbar province as they were returning home by way of Syria. It did not give the exact day of the killing, saying only that it was a few days ago.