Three blasts, including a suicide attack, have killed at least 17 people in and around the Iraqi capital, Baghdad, officials say.

The most deadly of Tuesday's explosions took place in Taji, 20km north of Baghdad, where a suicide bomber driving a car packed with explosives detonated his bomb near an army base, killing at least seven people and wounding 24.

Nasseer Rahman, a teacher, said he was sitting in a minibus waiting to pass the checkpoint when the bomb exploded about 120 metres away. He said dozens of cars were waiting in lines when the blast went off.

"As soon as the blast struck, we got off the minibus and ran to the site of the explosion," he said. "We saw several cars on fire and pools of blood, and everybody was screaming for help.''

Another car bomb exploded in a crowded market in the Shia neighbourhood of Shula, in the northwest of the capital, killing five people and wounding 13, police and hospital sources said.

"We received a call for us to head to the blast site. It was a car bomb. A woman was laying dead with a sack of groceries still beside her, and the wounded were screaming," said policeman Ghalib Ameer, whose patrol was called to Shula.

In Mahmudiya, a town 30km south of Baghdad, a car bomb attack near an army checkpoint killed five people, including two soldiers, and wounded 14 more.

Violence in Iraq has eased since the widespread sectarian carnage of 2006-2007, but Sunni armed groups still launch frequent attacks to reignite confrontation among the Shia majority, Sunni Muslims and ethnic Kurds.

Sunni protests

The latest attacks come amid rising ethnic and sectarian tension following the arrest last month of bodyguards assigned to the Sunni finance minister Rafia al-Issawi.

Thousands of Sunni protesters are camped out in western Anbar province in what is developing into a major challenge to Prime Minister Nouri al-Maliki, whose power-sharing government, split among Shias, Sunnis and Kurds, has been bogged down in infighting since the last US troops left a year ago.

The Shia prime minister is trying to ease protests that erupted a month ago after officials arrested members of the finance minister's security team on terrorism charges. Sunni leaders saw that move as a crackdown.

Since the fall of Saddam Hussein after the US-led invasion a decade ago, many Iraq Sunnis feel they have been marginalised by the Shia leadership and say Maliki is amassing power at their community's expense.

Maliki has appointed Shia Deputy Prime Minister Hussein al-Shahristani to investigate the protesters' demands.

Authorities said on Tuesday they had so far released more than 800 detainees unjustly held or whose sentences had ended.

But thousands of protesters, camped out on a highway in the Sunni heartland of Anbar, say they are determined to stay until their demands are met.

Sunni leaders want the modification of anti-terrorism laws and more control over a campaign against former members of Saddam's outlawed Baath party, both measures they believe unfairly target their minority community.