The attacker detonated an explosive vest at a police checkpoint in the historic city of Najaf, just 150 metres (yards) from the tomb of Imam Ali, one of the most revered figures of the Shia faith, police said.

"The total casualties are 35 killed and 94 wounded, including four Iranian visitors. One of them is in serious condition," said Doctor Munther al-Athari, the head of Najaf's health directorate.

A senior security official, speaking on condition of anonymity, said the bomber had attempted to approach the shrine but had been stopped by police.

"When he arrived at the last checkpoint, the police were suspicious of him and grabbed him. Once he was in their hands, he blew himself up, killing the five police guards at the checkpoint," the official said.

Further north, in Baghdad, seven police commandos including a senior officer were killed in a rebel ambush and six civilians were killed in the bombing of a popular restaurant, security and medical sources told AFP.

The Najaf bombing was immediately interpreted as the latest in a spate of attacks designed to further poison relations between Iraq's Shia Arab majority and the aggrieved Sunni Arab former elite.

US generals warned last week that sectarian bloodshed could push Iraq into civil war, despite attempts by the national unity government to restore order and promote a reconciliation plan.

Prime Minister Nuri al-Maliki's government has vowed to root out sectarian death squads and is attempting to persuade armed groups to join talks to reconcile the divided communities.

But attacks and counterattacks have continued, and on Thursday the health ministry said that in the last month alone the Baghdad mortuary had handled 1,850 corpses, most of them murder victims.

"The figure for June was 1,350 and this increased to 1,850 last month," ministry spokesman Qasim Yahia told AFP, adding that provincial mortuaries had also handled many dead, but he did not have the figures.

The sectarian bloodletting began in earnest in February after suspected Sunni militants blew up a revered Shia shrine in Samarra, triggering a wave of brutal revenge killing.

The Supreme Council for Islamic Revolution in Iraq (SCIRI) -- a powerful Shia religious party that is a pillar of Maliki's ruling coalition -- was swift to blame Sunni militants for the latest attack too.

"We call upon everyone to stop these attacks that target civilians, the aim of which is to create sedition and internal strife," party spokesman Aziz Zein al-Ali said.

"We believe that such an act was carried out by Saddamists (supporters of ousted leader Saddam Hussein's Sunni-dominated regime) and takfiris (Sunni religious extremists) who do not want stability in this country," he said.

An aide to Shia radical leader Moqtada Sadr seized on the deaths to demand that Shias be allowed to form self-defence committees, a move that would undermine the prime minister, who has vowed to disarm militias.

"We condemn and reject such acts near the shrine of the Imam. We call upon the security authorities in the city to take stringent measures," said Saheb al-Ameri, the head of Sadr's office in Najaf.