Loud explosions and heavy fighting rattled Baghdad on Sunday, as a new round of violence between US-Iraqi forces and insurgents broke out in the Iraqi capital, the heaviest for months.

A car bomb exploded on Sunday near a highway in western Baghdad, killing three Iraqi police officers and wounding four others, witnesses said.

"A number of police cars were chasing a suspect car, and when they managed to surround the car, the driver blew it up, killing three police officers including Col. Alaa al-Dein Bashir," MuhmoudAbdul-Allah, a witness told Xinhua.

Earlier in the day, heavy fighting erupted in Haifa street in central Baghdad between US forces and insurgents and lasted for three hours, killing at least 13 people and wounding 55 others, the Health Ministry said.

Witnesses said the casualty toll climbed when US helicopters fired at a crowd gathering around a burnt US tank in the area. Mazen al-Tomizie, a 26-year-old Palestinian journalist working for Dubai-based al-Arabiya TV was killed as he was reporting live from the scene, a colleague said.

A missile fired by a US chopper landed near Tomizie and several Shrapnels hit him fatally, the colleague said.

US and Iraqi National Guard forces later closed off all roads leading to the street and besieged the nearby cemetery area which is a usual hiding place for militants.

Also on Sunday, militants fired some 20 mortar rounds at the heavily-fortified Green Zone, the seat of the interim Iraqi government and the US embassy. The US military did not disclose the size of the damage.

And almost simultaneously, two drivers were shot dead when trying to ram their booby-trapped cars into the Green Zone and the Abu Ghraib prison in western Baghdad, killing themselves. The prison has been at the center of a scandal over the abuse of Iraqi detainees by US soldiers.

In another development, insurgents attacked a US military convoy on a road to the Baghdad international airport, destroying threehamvees and causing unknown casualties, a Xinhua photographer witnessed.

The US vehicles were still on fire at around 11:30 a.m. (07:30GMT).

Abu Musaab al-Zarqawi's group swiftly claimed responsibility for attacks on the Green Zone and the Abu Ghraib prison. The group has also issued a new threat against Iraqi Prime Minister Iyad Allawi in a purported taped message posted on the Internet.

"We will make sure that the traitor Allawi gets his due. Youtraitor, stop pretending and wait, because we will know how to be more cunning than you," said the taped voice.

The United States has offered a 25-million-dollar reward for the capture of Zarqawi, whose Tawhid and Jihad (Unity and Holy War)group has claimed many attacks and kidnappings in Iraq.

Source: Xinhua