Suicide bombers set off simultaneous attacks on Shia Muslim shrines crowded with pilgrims in Kerbala and Baghdad Tuesday.

Chanting "God is Greatest," huge crowds gathered yesterday to mourn at least 271 people killed in a wave of bombings in two Iraqi cities, bearing flower-laden coffins aloft through the bustling streets.

A Shia procession in Pakistan's Quetta was attacked by gunmen and a suicide bomber, triggering chaotic shootouts and mob rampages that claimed 50 lives.

"Two gunmen on top of a building opened indiscriminate fire at the same time as a suicide bomber walked into the crowd and blew himself up. Another two gunmen accompanying the bomber on the ground then sprayed bullets into the crowd," a Quetta-based intelligence official, who could not be named, told AFP.

"Police then joined in the firing, not knowing where the shots came from they started firing in all directions, up and down.

Pakistani officials did not believe the carnage in Quetta and Iraq was linked, although both countries harbour networks of radical Islamic militants with deep hatred for the United States and its allies.

In Iraq, as the coffin of one local Shia cleric passed, draped in a black flag with verses from the Quran, bystanders reached out to touch it and then held their fingers to their lips whispering "Hussein," the name of a revered Shia martyr.

At least five bombs tore through Kerbala Tuesday morning, just as a major Shia religious festival was concluding, killing close to 200 people and wounding 235, according to a senior local cleric. The US military said one of the blasts was caused by a suicide bomber.

Coordinated strikes against Shia worshippers in Baghdad killed over 60, according to the latest Health Ministry figures.

Unofficial casualty reports, however, put the toll in the two cities as high as 223.

US officials and Iraqi leaders named an al-Qaeda-linked militant, Abu Musab al-Zarqawi, as a "prime suspect" for the attacks, saying he seeks to spark a Sunni-Shiite civil war to wreck US plans to hand over power to the Iraqis on June 30.

But some Shias lashed out at US forces. Iraq's most powerful Shiite cleric, Grand Ayatollah Ali al-Hussein al-Sistani, blamed the Americans for not providing security.

A letter purporting to come from Osama bin Laden's al Qaeda network denied any role in Tuesday's anti-Shia Muslim explosions in Iraq and blamed the attacks on the US.

The letter, signed by the Abu Hafs al-Masri Brigades with "al Qaeda" in parenthesis, was sent to the London-based al-Quds al-Arabi newspaper. It was obtained by Reuters yesterday.

In Pakistan, most of the Quetta victims were shot in the cross-fire, the intelligence official said.

"There were people carrying weapons within the procession, they probably targeted the police," he said.

Three of the four gunmen were shot dead while the other was wounded by a bullet in his head. He survived and is under arrest.