Multiple bombings killed at least 107 people and injured 131 others amid relentless bloodbath in and around Baghdad on Thursday, defying the ongoing security crack down designed to curb violence in the warn-ravaged country.

In the bloodiest violence, a suicide bomber killed at least 60 people in a very crowded market in northeastern Baghdad, an Interior Ministry source told Xinhua.

Another 40 were also injured in the attack while the bomber wearing an explosives vest blew himself up in the Shalal market inal-Shaab neighborhood, the source added on condition of anonymity.

Almost simultaneously, four apparently coordinated car bombings hit Khalis, a predominantly Shiite town some 80 km north of Baghdad, local police told Xinhua, adding at least 47 people were killed and 91 others were injured.

According to details provided by police, one car bomb went off near a bank shortly before a second near a mosque, a third near a checkpoint and a fourth near a court.

Khalis, a town in Diyala province, has been plagued by sectarian violence between Sunnis and Shiites.

The latest upsurge of violence came days after sectarian bloodshed in Iraq's northern town of Tal Afar, some 420 km northwest of Baghdad, which claimed over 100 lives.

On Tuesday, 85 people were killed and 138 wounded in twin car bombings in a Shiite district in Tal Afar, which triggered subsequent reprisal attacks by Shiite militants and police, leaving at least another 70 Sunni residents killed.

Since Feb. 14, US forces and Iraqi government have launched the last-ditch security crackdown in the capital to prevent the country from spiraling toward a full-scale civil war between Shiite majority and Sunni minority.

There have been signs of progress on the ground. However, despite some upbeat Iraqis, many of the people are still skeptical how long the relative calm could last. US and Iraqi officials are also very cautious about the plan and called for more patience.

Some analysts warned that Shiite militias and Sunni insurgents may have changed their tactics by temporarily lying low or hiding outside Baghdad until the troop surge ends, so it is hard to judge whether it is a sustainable progress.

In other development on Thursday, the new US ambassador to Iraq, Ryan Crocker, was sworn in at the US embassy in Baghdad's heavily fortified Green Zone.

The swearing-in ceremony was held at the embassy, the once Republican Palace of Saddam Hussein, and was attended by US Lieutenant General David Petraeus, the commander of US forces in Iraq, and embassy officials, US embassy spokesman Lou Fintor said.

Crocker told the ceremony that his country is facing "historic challenges" in Iraq with insurgents and militia continuing to threaten security in Baghdad and across the country.

He emphasized that his mission in Iraq is not impossible, saying "all of these (challenges) will be very hard, but if I thought it was impossible I would not be standing here today."

The 57-year-old veteran diplomat pledged to support the government led by Shiite Prime Minister Nuri al-Maliki, but warned that the Iraqi leader must take all necessary steps to unite the war-torn country.

"We must stand by the Maliki government and all Iraqis who seek a better future and remain committed to their success," Crocker said.

Crocker can speak fluent Arabic and has been ambassador in several Arab countries and Pakistan in the past.

He arrived in Iraq late on Tuesday, replacing his predecessor Zalmay Khalilzad, who has been nominated by US President George W. Bush as US ambassador to the United Nations.

(Xinhua News Agency March 30, 2007)