BAGHDAD - A series of bombs killed at least 43 people in and near Baghdad on Saturday, police said, in one of the bloodiest days in Iraq since a US military air strike killed Abu Musab al-Zarqawi 10 days ago.
The violence, a day after a suicide bomber killed 10 people in a Baghdad Shi'ite mosque, came despite a security crackdown in the Iraqi capital and followed a vow by al Qaeda's new leader in Iraq to avenge the death of his predecessor on June 7.
The attacks, which included at least four Baghdad car bombs, posed a fresh challenge to Prime Minister Nuri al-Maliki, who is under pressure to ease a violence that has killed thousands of Iraqis and complicated plans for a US troop withdrawal.
In the deadliest attack, a car bomb struck an Iraqi police checkpoint in a Shi'ite area southwest of Baghdad, killing at least 12 people and wounding 38, police said.
Earlier, another car bomb targeting Iraqi army and police killed 11 people.
Moving to fulfill promises he will use "maximum force against terrorism," Maliki launched a security operation on Wednesday with 50,000 Iraqi troops backed by 7000 US troops to pile pressure on al Qaeda in Iraq.
But the sweep, mounted one day after US President George W. Bush made a surprise visit to Baghdad to bolster Maliki's month-old government, has failed to stop attacks.
In a fresh reminder of the huge task Maliki faces despite a claim by Iraq's national security adviser that al Qaeda's days were numbered, militants hit security forces across the capital and bombed at least two crowded markets, including one in central Baghdad that left six people dead.
Attacks on crowded markets are a common tactic used by al Qaeda as part of what US officials say is a campaign to ignite a sectarian civil war between majority Shi'ites and Saddam Hussein's once-dominant Sunni Arab minority.
In the town of Mahmudiya just south of the capital, a car bomb targeting an Iraqi army checkpoint killed seven people.
US military helicopters and divers searched for two US soldiers missing after an attack on Friday in which one American soldier was killed in the insurgent bastion of Yusufiya in the "Triangle of Death" south of Baghdad.
"We are using all available assets, Coalition and Iraqi - ground, air and water - to locate and determine the duty status of our soldiers," the US military said.
More than 2500 US soldiers have died in Iraq since the US-led invasion in 2003.
Bush, facing sagging domestic support over the war, said on Saturday the United States had gone too far to abandon Iraq and encouraged other nations to make good on US$13 billion ($21 billion) in pledges to help the new Iraqi government.
"It is vital for the Iraqi people to know with certainty that America will not abandon them after we have come this far," Bush said in his weekly radio address.
Bush gave no hint of any imminent drawdown of the 129,000 US troops in Iraq despite domestic political pressure to do so before crucial congressional elections in November.
"We face determined enemies who remain intent on killing the innocent, and defeating these enemies will require more sacrifice and the continued patience of our country," he said.
The US military has said it expects al Qaeda's new leader, who it identified as Abu Ayyub al-Masri, to use the same tactics as Zarqawi, a Sunni Arab militant.