Early morning bombings in Iraq have killed at least eight people as United States and Iraqi officials promised to crack down on violence and sectarian attacks.

Six workers were killed and 12 others were injured in southern Baghdad Monday when a van they were riding in was hit by a bomb at about 8 a.m. local time in the city's violent southern neighbourhood of Radon, Iraqi police said.

Bombings in the area have become common in recent weeks as sectarian violence escalates.

In a separate incident, a roadside bomb detonated next to a police patrol east of Kirkuk, but missed and struck a civilian car, police said.

One person was killed in the blast and two more were reported injured.

The deaths come as Iraqi and U.S. officials plan a security crackdown after al Qaeda vowed in an Internet message on the weekend to carry out "major attacks" following the coalition air strike that killed al Qaeda in Iraq leader Abu Musab al-Zarqawi on Wednesday.

Officials hope his death will slow the sectarian violence that kills dozens each day.

Meanwhile, U.S. President George Bush began a two-day summit Monday at Camp David with his top advisers to discuss a new strategy for Iraq.

The talks will include reconstruction projects and initiatives to curb violence in the war-torn nation.

Bush will meet with Iraqi Prime Minister Nouri al-Maliki on Tuesday.

The pair hope to set a firm agenda for security plans and repairing infrastructure such as Iraq's electricity system, which has led to dissatisfaction with U.S. forces. Most residents in Baghdad have as little as 30 minutes of electricity a day.

Al-Maliki's new security team has also moved ahead with a plan to restore security in Baghdad, which has suffered most from suicide attackers, roadside bombs and sectarian death squads. The government will announce the plan in days.

On Sunday, Iraqi officials released about 200 detainees from Abu Ghraib prison. Al-Maliki has promised to release 2,000 detainees from U.S.-run prisons by the end of the month -- the largest total since the U.S.-led invasion began in March 2003.

Sunnis frequently complain of random detentions and maltreatment at the hands of the Shiite-led government.

The prisoner releases are seen as a key step toward dampening the Sunni-led insurgency.

With files from The Associated Press