A suicide bomber detonated a belt of explosives Thursday near a highly revered Shiite shrine in southern Iraq, killing at least 35 people and injuring 122, an official said.

The bomber blew himself up while being patted down by police near the Imam Ali mosque in the Shiite holy city of Najaf, said Dr. Munthir al-Ithari, the head of the city's health directorate.

Shiite religious leaders in Najaf accused Sunni loyalists of former dictator Saddam Hussein of carrying out the attack.

"We hold Takfiris (Sunni extremists) and Saddamists directly responsible for this horrible crime ... at the same time we hold those who embrace terrorism in Iraq and the countries supporting it as responsible," the statement said.

The Iraqi army said the death toll was 35, with 122 injured.

Prime Minister Nouri al-Mailiki, a Shiite, denounced the bombing as a "barbaric massacre conducted by Takfiris (Sunni extremists) and Saddamists who are seeking to inflame sectarian" passions. A statement by the collective Shiite leadership also issued a similar condemnation.

A Sunni insurgent group, Jamaat Jund al-Sahaba, or Soldiers of the Prophet's Companions, claimed responsibility for the bombing in an Internet posting. It warned Shiites to stop killing unarmed Sunnis, "otherwise wait for such operations that will shake your regions like earthquakes."

In other violence, 18 people were killed across the country, most of them in Baghdad, including four policemen who died in a gunfight with insurgents. Five bodies were also found Thursday.

The Najaf bombing occurred at about 10:30 a.m. in a market packed with pilgrims and shoppers in front of the Imam Ali mosque, which contains the tomb of Prophet Muhammad's son-in-law, Ali. It is one of the world's most sacred shrines for Shiites, the minority sect of Islam.

Shakir Obeid Hassan, who was injured in the blast, said the suicide bomber was stopped at the last police checkpoint before the shrine, which was untouched, though all the stores facing the shrine were damaged, he said.

"Before I reached the checkpoint, only a few (feet) from the shrine, I heard a huge explosion. Something hit me on the head and I fell. I couldn't hear for a while but I saw bodies and human flesh everywhere," Hassan, 51, said from his hospital bed.

The Grand Market, directly in front of the shrine's entrance, is a wide road with shops lining both sides selling perfumes, jewelry, clothes and religious souvenirs, including rings with pictures of Ali and his son Hussein.

The aftermath of the bombing was a scene of carnage. Indistinguishable debris, boxes of perfume bottles, sandals and worry beads littered the bloodied street. Volunteers picked up human remains and washed away the thick pools of blood.

Najaf, 100 miles south of Baghdad, is a major pilgrim destination for Shiites around the world, especially from neighboring Iran, which is predominantly Shiite like Iraq. Al-Ithari said one Iranian woman was among the 33 dead and nine Iranians among the 108 injured.

Najaf was the scene of heavy fighting in 2004 between U.S. forces and the Mahdi Army of radical cleric Muqtada al-Sadr, until the Shiite clerical hierarchy convinced the militiamen to give up.

Since then the city — considered the world center of Shiite theology — had been tightly controlled by police and Shiite guards, including former militiamen. The late Iranian leader Ayatollah Ruhollah Khomeini lived for years in exile in Najaf and Hassan Nasrallah, the head of Hezbollah, studied there.

Generations of tensions between Shiites and Sunnis turned into bloodshed after a Feb. 22 bombing of a Shiite shrine in Samarra. Extremists among both communities have been embroiled in reprisal attacks since then, fueling fears that Iraq was on the verge of civil war.

A bombing near another Shiite shrine in Kufa, the twin city of Najaf, on July 18 killed 53 people. Thursday's explosion is the first attack near the Imam Ali shrine.

The Shiite Endowment urged people not to be incited by "this terrorist and criminal attack." The attack shows "blind hatred and insistence on blasphemy," the endowment said in a statement, and called on people "to remain united" to thwart sectarianism.

Sectarian clashes have largely occurred in the Baghdad area, where about 1,500 violent deaths were reported last month, a dramatic rise from about 1,000 in January. Most of the deaths were believed to be the result of sectarian feuding.

The bloodshed has dashed U.S. hopes for an early drawdown in the 127,000-member U.S. military force here. Instead, the U.S. military is rushing about 12,000 American and Iraqi soldiers to Baghdad.

Iraq's National Security Adviser Mouwaffak al-Rubaie said police arrested 20 Al Qaeda members and killed one around the country in recent few days.