BAGHDAD — Five suicide bombers struck Shiite marketplaces in northeast Baghdad and a town north of the capital at nightfall yesterday, killing at least 122 people and wounding more than 150 in one of Iraq’s deadliest days in years.

The savage attacks came as a new American ambassador began his first day on the job, and Senate Democrats ignored a veto threat and approved a bill to require President Bush to start withdrawing troops.

At least 178 people were killed or found dead yesterday, which marked the end of the seventh week of the latest American-Iraqi military drive to curtail violence in Baghdad and surrounding regions.

The suicide bombers hit markets in the Shiite town of Khalis and the Shaab neighborhood in Baghdad during the busiest time of the day, timing that has become a trademark of what are believed to be Sunni insurgent or Al Qaeda suicide attackers.

Three suicide vehicle bombs, including an explosives-packed ambulance, detonated in a market in Khalis, 50 miles north of the capital, which was especially crowded because government flour rations had just arrived for the first time in six months, local television stations reported.

At least 43 people were killed and 86 wounded, police said.

In the north Baghdad bombings, two suicide attackers wearing explosives vests blew themselves up in the Shalal market in the predominantly Shiite Shaab neighborhood. At least 79 people were killed and 81 wounded as they jammed the market to buy provisions on the eve of the Islamic day of rest and prayer.

The carnage in Iraq cast a shadow over Ryan Crocker’s first day as ambassador. He takes over in the midst of the American-Iraqi security sweep, for which Mr. Bush committed nearly 30,000 additional troops to dampen what had become uncontrollable violence in the capital.

The Senate’s rare rebuke to a wartime commander in chief came in a 51–47 vote to provide $123 billion for the wars in Iraq and Afghanistan. Senators also ordered Mr. Bush to begin withdrawing troops within 120 days of the bill’s passage, and set a nonbinding goal of ending combat operations by March 31, 2008.

“President Bush’s policy is the right one. There has been progress; there is also much more to be done,” the 57-year-old Mr. Crocker said at his swearing in at the American Embassy in Saddam Hussein’s former Republican Palace which is now in the heart of the heavily guarded Green Zone.

Violence has increasingly erupted in towns and cities outside the capital in recent weeks, as insurgent fighters take their fight to regions where American and Iraqi forces are thinly deployed. The American military and its diplomats have voiced cautious optimism about the sweep and emphasized that the full American surge force would not be in place until June. Mr. Crocker brought the same message.