Two suicide bombers blew themselves up Tuesday in a crowd of Shi'ite pilgrims streaming toward a shrine south of Baghdad, killing up to 90 people, police said. The coordinated attack happened on a main street in Hillah, about 95 kilometers (60 miles) south of Baghdad, said Capt. Muthana Khalid. More than 150 others were wounded in the blasts, he said. Earlier, nine American soldiers died in explosions north of Baghdad, the US military announced Tuesday after the deadliest single day for US troops in Iraq in nearly a month. Six soldiers died when a bomb exploded Monday near their vehicles during a combat operation in Salahuddin province, the military said. Three others were wounded in the blast. Another three soldiers died the same day in a roadside bomb attack in Diyala province northeast of Baghdad. Shi'ite pilgrims, too, came under attack as they streamed south, mostly on foot, toward a shrine in Karbala ahead of a weekend holiday. Police said at least 20 were killed Tuesday in shootings and bombings along the way. In Baghdad, US forces continued their push into Sadr City, home to 2.5 million of the city's poorest residents as well as fighters loyal to anti-American cleric Muqtada al-Sadr. Some 600 American soldiers searched the neighborhood's northwest quadrant, knocking on doors and searching homes, according to an Associated Press reporter traveling with them. The US forces are seeking a "reconciliatory approach" to avoid sparking a backlash on the streets, said Col. Richard Kim. One small gesture seemed to offer appreciation: a child offering soldiers ice cream bars. Monday was "a very traumatic day" for US troops in Iraq, said Lt. Col. Michael Donnelly, a spokesman for US forces in northern Iraq. "Our hearts and prayers are with the families right now in their time of loss, and our resolve is stronger to accomplish our mission here," Donnelly said. It was the deadliest day for Americans in Iraq since Feb. 7, when 11 troops were killed - seven when their helicopter was shot down north of Fallujah and four others in combat operations. The highest daily US death toll since the Iraq war began was Jan. 26, 2005 when 37 Americans died in attacks. Both provinces where Monday's deaths occurred are Sunni-dominated. Saddam Hussein's clan hails from Salahuddin, and the late al-Qaida in Iraq leader Abu Musab al-Zarqawi was hiding out in Diyala when he was killed by a US airstrike there last summer. Violence has fallen in Baghdad, where a joint US-Iraqi security crackdown was in its third week. But US military officials say insurgents have fled the capital for outlying areas, where attacks are on the rise. Direct attacks on US forces in Diyala are up 70 percent since last July, according to figures provided by the US military. A suicide car bomber shattered the capital's relative calm Monday, striking a famous book market in the city's oldest quarter and killing at least 38 shoppers. Iraqi Prime Minister Nouri al-Maliki condemned the attack on Tuesday in a statement issued by his office. The bombing was seen as an effort by Sunni insurgents to bring major bloodshed back into the capital and into the lap of its Shiite-dominated government. The provocation could also erase Washington's plans for stability during a surge of more than 20,000 additional troops into Baghdad. At least 20 Shiite Muslims were killed on their trek southward Tuesday toward Karbala, where they would mark the end of a 40-day mourning period after the death of the Prophet Muhammad's grandson. The deadliest attack was in the south Baghdad neighborhood of Dora, where gunmen pumped bullets into a minibus, killing all eight passengers inside, police said. A car bomb nearby killed two others hours later, they said. Five pilgrims were killed and more than a dozen wounded in two car bomb attacks in Baghdad's Yarmouk section, police said. Mohammed Mahdi al-Bayati, a Shiite member of parliament, said four of his relatives were killed when his convoy was attacked about 100 kilometers (60 miles) north of Baghdad, en route to Karbala. Two shootings in Latifiyah, 30 kilometers (20 miles) south of Baghdad, left three people dead, police said. Roadside bombs killed one person each in northern Baghdad and in Youssifiyah, 20 kilometers (12 miles) south of the capital, police said. All the neighborhoods where Shiites were killed Tuesday were Sunni. Last year, Sadr's Mahdi Army militia provided security to some pilgrims during the commemorations known as Arbaeen. In past years, militiamen "played a role in protecting the pilgrims and the attacks were fewer and less effective, but this year things are different," said Bahaa al-Araji, another Shiite parliament member. "The government bears some responsibility for this because it has not provided enough security forces to protect the pilgrims," al-Araji said. "This indicates some shortcomings in the Baghdad security plan." Meanwhile, Iraqi army units were preparing to deploy along major routes to ensure pilgrims' safety, according to a Defense Ministry statement issued Tuesday. "The Defense Ministry hopes that the citizens will continue the rituals of the pilgrimage safely under efficient security protection," the statement said. The nine US deaths Monday brought to 20 the number of Americans killed in Iraq this month. At least 3,184 members of the US military have died since the beginning of the Iraq war in March 2003, according to an Associated Press count. The figure includes seven military civilians. At least 2,561 died as a result of hostile action, according to the military's numbers.