Muqtada Sadr’s statement signaled growing impatience among Shiites over continued bombings by insurgents and the government’s failure to protect them.

Friday’s bombings — most targeting Shiite places of worship as crowds were at prayer — killed 72 people in Iraq’s bloodiest day so far this year in an apparent backlash by the Sunni-led insurgency after the slaying of the top two Al-Qaeda leaders last weekend.

Nobody claimed responsibility for the attacks, but Iraqi officials were quick to blame Al-Qaeda in Iraq, which frequently targets Shiite mosques and processions in a bid to stoke new sectarian bloodshed. Prime Minister Nuri Al-Maliki said the insurgents were fighting back after the deaths of their two leaders.

Sadr, whose forces have frequently clashed with the Americans, issued a statement late Friday calling on “believers” to join the Iraqi army and police “to defend their shrines, mosques, prayers, markets, houses and their towns.” He stopped short of mentioning the Mahdi Army, his once-powerful militia, which used to respond to such attacks with raids on Sunni areas. Several advisers said Sadr was offering his assistance to the government in a rare show of magnanimity to Al-Maliki.

The two men were once allies but became rivals after Al-Maliki backed US-Iraqi offensives in 2008 that crushed Sadr’s fighters and forced him to declare a series of cease-fires.

The cleric, who is widely believed to be based in Iran, has re-emerged as a prominent politician and a potential kingmaker after his followers fared well in the inconclusive March 7 parliamentary vote. That left Al-Maliki and his secular rival Ayad Allawi jockeying for allies to give them the necessary majority support to govern.

The protracted political wrangling has raised fears of sectarian violence akin to that seen at the height of the war. US and Iraqi officials have acknowledged that insurgents maintain the ability to stage high-profile bombings while noting the Shiites have not resumed retaliatory attacks.

A Sadrist who won a seat in the new parliament, Hakim Al-Zamili, emphasized that Sadr’s statement was not meant to supplant the Iraqi military or put armed supporters on the streets.

Sadr urged Iraqi leaders “not to be pulled toward the malicious American plans that intend to pull Iraq into wars and fighting in order to find the pretext for staying on our holy lands.” He appeared to be appealing for a renewed commitment, despite continued violence, to stick to a deadline for all US forces to withdraw from Iraq by the end of 2011.

Al-Zamili — himself once imprisoned for alleged links to Shiite death squads although the charges were eventually dropped — said he and other Sadrists had to intervene when the Iraqi military arrived on the bomb scene Friday because people in the neighborhood were so angry that he feared a serious altercation between residents and military personnel.