Baghdad, Iraq - A bomb that killed five people in the Baghdad stronghold of a Shi'ite militia on Thursday and a machinegun attack on the car of a leading Sunni politician kept sectarian tension crackling after a week of bloodshed in Iraq.
The Mehdi Army of radical Shi'ite cleric Moqtada al-Sadr said it would defend its neighbourhoods after a bomb, possibly a suicide attack, killed five and wounded eight in a minibus in the heart of Sadr City, a Shi'ite slum in eastern Baghdad.
The area has been relatively immune from Sunni insurgent attacks, possibly because Sadr has sought alliances with Sunnis who share his nationalist, anti-American posture.
In mainly Sunni west Baghdad, gunmen ambushed and destroyed the armoured limousine of Adnan al-Dulaimi, a veteran leader of the main Sunni political bloc, the Iraqi Accordance Front, a party spokesman who was present said. A bodyguard was killed.
Dulaimi himself had only just got out of the car because it had a flat tyre. As he resumed his journey in another vehicle, his guards were surrounded by assailants firing assault rifles.
A senior official in Sadr's movement accused Sunni Islamists allied to al Qaeda of bombing the minibus and said the Mehdi Army would respond.
"Today, the terrorists have targeted Sadr City because it has a Shi'ite majority which shows the extremists want to fight Shi'ites wherever they are," Hazim Araji told Reuters.
"We are going to coordinate with Iraqi army and police but the Mehdi Army is going to have a key role in providing protection," he said, adding that some approaches to the slum area that is home to perhaps two million people may be blocked.
Dozens of militiamen swarmed into the streets after the bombing.
The Shi'ite-led interim government of Prime Minister Ibrahim al-Jaafari has struggled to respond to violence since the bombing of a Shi'ite shrine in Samarra on February 22.
UNDER PRESSURE
At least 450 people, by the most conservative official estimates, have been killed in sectarian bloodshed since then.
The government has ordered thousands of police onto the streets of Baghdad, backed up by U.S. troops, but their effectiveness is untested and their loyalties are uncertain in the face of sectarian militias to which many once belonged.
Jaafari is also under pressure from Sunni, Kurdish and other leaders threatening to seek his removal as the price for joining a national unity coalition -- seen by U.S. officials as the best hope for stability that would allow American troops to go home.
Opponents have also questioned why Jaafari failed to act on a warning from his own security staff about possible attacks on shrines, given two weeks before the Golden Mosque was destroyed.
U.S. and Iraqi leaders accuse al Qaeda militants of bombing the shrine to drag Shi'ites into a civil war that would wreck U.S. plans. Some Sunnis say Iranian-backed Shi'ites did it to justify reprisals against the Sunni Arab minority.
Sadr, a youthful cleric with a following among poor Shi'ites, led two uprisings against U.S. forces in 2004 that won him allies among Sunni rebels. But many Sunnis now blame his Mehdi Army militia for attacks on Sunni mosques this past week.
Sadr denies any involvement in reprisals against Sunnis and has called for joint Sunni-Shi'ite prayer services.
But appeals for calm have not halted the bloodshed.
Gunmen killed a Sunni imam in a mosque in the southern, mainly Shi'ite, city of Basra at dawn, the Muslim Clerics Association, a Sunni organisation, said.
Six Iraqi soldiers and three policemen were killed at a checkpoint in northern Iraq late on Wednesday night in an attack that again highlighted weaknesses in the U.S.-trained forces.
The assault, near Saddam Hussein's home town of Tikrit, took place hours after four police officers travelling in a convoy of unarmed recruits were killed in an ambush north of Tikrit.
A roadside bomb exploded near a police station in southeastern Baghdad, killing three people and wounding 10.
Three years after he invaded Iraq to topple Saddam, the crisis has jeopardised President George W. Bush's hopes of pulling out some of his 133,000 troops before mid-term elections in November. It also threatens turmoil across the Middle East.