A bomber has killed at least six people and wounded 21 in one of Baghdad's largest mosques, despite a security crackdown putting large numbers of Iraqi and US troops on the streets.

The bomber attacked the Baratha mosque barely an hour before Friday's prayers, a security source said on Friday.

The mosque, which is used by members of Iraq's Shia, had been fired at several times since the 2003 US-led invasion of Iraq.

On April 7, a triple bombing hit worshippers just as they were leaving the mosque, killing 90 and wounding 175.

Also, a mortar barrage struck a commercial area north of Baghdad on Friday, killing at least two people and wounding 16, police Lieutenant Muhammad Khayun said.

The attack occurred at 1.30pm on a street with many shops in the northern suburb of Saba Abkar, near the Taji air base,

Security measures

The new violence came despite a clampdown in the capital ordered by prime minister Nuri al-Maliki since Wednesday that saw vehicles banned from the capital's streets during prayer times, and a large number of Iraqi and US soldiers out on patrol.

The crackdown, dubbed Operation Forward Together, is one of the largest since the US-led invasion of 2003 and is directed at exploiting any power vacuum in anti-US and US backed Iraqi government fighters' ranks after the death of Iraq al-Qaeda frontman Abu Musab al-Zarqawi in a US air raid last week.

It follows similar counter operations after the two previous prime ministers, Iyad Allawi and Ibrahim al-Jaafari, took power.

The defense ministry said 160 additional checkpoints had been set up in Baghdad and 26,000 Iraqi soldiers, 23,000 Iraqi police and 7,200 coalition troops were deployed on the streets.

The security plan includes house-to-house searches in areas suspected of harboring fighters as well as a crackdown on civilians carrying weapons.

Hasty

Before the mosque bombing, the Iraqi government and its US backers said the crackdown was successful.

The US military said on Thursday it had killed 104 and captured 759 in a total of 452 operations since al-Zarqawi's death.

Muwaffaq al-Rubaie, Iraq's national security adviser, said: "it was the beginning of the end of al-Qaeda in Iraq.

"We believe al-Qaeda in Iraq was taken by surprise; they did not anticipate how powerful the Iraqi security forces are and how the government is on the attack now," he said.

But outside the capital too, violence raged on Friday.

Just south of Baghdad, in an area dubbed the Triangle of Death, for the frequency of attacks, four people were killed and 10 kidnapped in separate incidents, police said.

In the city of Baquba, north of the capital, a woman and  her four children were killed overnight when a bomb went off in a neighbor’s house, police said.

Photo Caption

Soldier mans Baghdad check point