At least six people were killed when a suicide car bomber hit Iraq's interior ministry on Monday in the latest attack since a crisis erupted between the country's Shi'ite-led government and Sunni leaders a week ago.

Shi'ite Prime Minister Nuri al-Maliki ordered the arrest of Iraq's Sunni vice president last Monday and asked parliament to fire his deputy, triggering turmoil that threatens a new wave of sectarian strife just after the last U.S. troops withdrew.

The blast occurred when the bomber drove his vehicle into a security cordon outside the Interior Ministry in central Baghdad, detonating an explosion that left dead and wounded on the ground and set fire to nearby vehicles, police said.

The attack on Bab al-Sharji street followed Thursday's wave of explosions in mainly Shi'ite areas across the Iraqi capital in which at least 72 people were killed.

When I went outside I found my colleagues, some of them were killed, others were on the ground, many cars were burned, the policeman on the watchtower looked like he was killed when he was hit in the head, Zaid Raheem, a police guard, said.

Six people, including four policemen, were killed and 34 others were wounded, police and hospital sources said.

A senior police source said authorities believed insurgents were targeting the ministry because of the announcement of the arrest warrant for Sunni Vice President Tareq al-Hashemi.

He has left Baghdad for semi-autonomous Iraqi Kurdistan, where he is unlikely to be handed over to central government officials immediately.

REGIONAL WORRIES

The crisis threatens to scuttle an uneasy power-sharing government that splits posts among the Shi'ite National Alliance coalition, the mostly Sunni-backed Iraqiya bloc and the Kurdish political movement.

Iraq's Sunni minority have felt marginalised since the rise of the Shi'ite majority after the 2003 U.S.-led invasion that toppled Sunni dictator Saddam Hussein, and many Sunnis feel the political deal has pushed them aside.

Turmoil in Iraq would have a wider impact in a region where a crisis in neighbouring Syria is taking on a more sectarian tone and Shi'ite Iran, Turkey and Sunni Arab Gulf states are jockeying for influence.

U.S. officials, diplomats and Iraqi politicians have been in talks to end the dispute that threatens to push Iraq back into the kind of sectarian violence that took the OPEC member to the edge of civil war a few years ago.

U.S. Vice President Joe Biden on Sunday spoke with Maliki and Iraqi Kurdistan Regional Government Masoud Barzani about the spat, urging dialogue among leaders, and expressing condolences over violence in Baghdad.

Biden played a diplomatic role during the U.S. military's departure from Iraq, travelling to the country and discussing signs of rising sectarian tension with Iraqi leaders.

U.S. forces withdrew fully from Iraq after almost nine years on December 18.

Thursday's blasts included at least one suicide car bomb and multiple roadside bombs.

(Additional reporting by Suadad al-Salhy; Writing by Serena Chaudhry; Editing by Louise Ireland and Patrick Markey)