Most of the victims of the blast at the School of Economy and Administration were students, about half of them women, according to a spokesman for the nearby Imam Ali hospital.

"They sold us out," one man cried as some students collected body parts they said would be buried on the school grounds.

The attacker struck at the college's main gate, and the walls on both sides were splattered with blood and bits of flesh.

There were fewer students than usual, however, owing to mid-term holidays.

The college is part of the renowned Mustansiriyah University and lies a few kilometres (miles) north of the main campus, near the Shia stronghold of Sadr City.

The university was struck by a twin bomb attack on January 16 that killed at least 70 people and wounded around 140.

On Sunday, the college annex was sealed off by Iraqi and US troops, but parents came in tears to search for sons and daughters at the scene, where papers and books littered the ground along with glass from scores of broken windows.

Founded in the 13th century, Mustansiriyah University was attended by executed dictator Saddam Hussein's half-brother Barzan Ibrahim al-Tikriti, who was hanged one day before the January bombing for crimes against humanity.

Elsewhere in the city, two rockets slammed into a Shia enclave in southern Baghdad yesterday, killing at least 10 people, and two people died in an explosion near the heavily protected Green Zone, police said.

The attacks came following an exchange of artillery and mortar fire between US troops and suspected Sunni insurgents south of the capital where a major security operation launched earlier this month has tried to cripple militant factions and sectarian killings.

The Katyusha rockets hit Abu Dishir, a Shia area surrounded Sunni neighbourhood, during the busy morning shopping hours.

Earlier, a bomb exploded near the edge of the fortified Green Zone, which houses the US and British embassies and key Iraqi government offices. The blast was about 100 yards from the Iranian Embassy, but authorities did not believe it was targeting the compound.

Iraq's interior ministry, meanwhile, raised the toll from a suicide truck bombing in the violence-wracked Anbar province on Saturday to 40 dead and 65 injured.

The attack on worshippers leaving a mosque in Habbaniyah, about 50 miles west of Baghdad, was believed linked to escalating internal Sunni battles between insurgents and those who oppose them.

US military envoys and pro-government leaders have worked hard to sway clan chiefs and other influential Anbar figures to turn against the militants, who include foreign jihadis fighting under the banner of al-Qaeda in Iraq. The extremists have fought back with targeted killings and bombings against fellow Sunnis.

The imam of the mosque attacked Saturday had spoken out against extremists most recently in Friday's sermon, residents said. Many people in the neighbourhood work for the Iraqi military and police forces, who frequently come under militant attack.

"There is no safe shelter for all outlaws," said Prime Minister Nouri al-Maliki, who reported that 426 militants have been captured since the Baghdad security campaign began Feb. 14.

But the crackdown also has sent Sunni insurgents fleeing the city to the nearby province of Diyala, which has emerged as a new and busy front for US troops.

It has become so volatile that the Pentagon may delay plans to turn over control of Diyala to the Iraqi military by the end of the year, Maj. Gen Benjamin Mixon told The Associated Press.

"The potential is there" to hand over Iraq's other 17 provinces "except in Diyala, where the future remains in question," said Mixon, commander of US forces in northern Iraq, which includes Diyala.

Diyala, northwest of Baghdad, is known as "Little Iraq" because of its near-equal mix of Sunni and Shia Arabs as well as Kurds the country's three major groups. al-Qaeda in Iraq leader Abu Musab al-Zarqawi, a Jordanian, was killed in a US airstrike in Diyala last year. Sunni extremists claim Diyala's capital, Baqouba, as the seat of an Islamic state in Iraq. (AFP, AP)