A female suicide bomber infiltrated a crowd of Shi'ite pilgrims and blew herself up, killing at least 38 people and wounding at least 72 in Baghdad on Sunday, Iraqi officials said. The bomber struck a checkpoint outside the Imam Moussa Al-Kadhim shrine in Kadhimiya, a mainly Shi'ite area of Baghdad, as Shi'ites prepared for the Ashura holiday this week. Many of the casualties were pilgrims from Iran, security spokesman Major-General Qassim Moussawi said. “There were bodies everywhere, some of them missing legs and arms,” said eyewitness Said Qassim, who was distributing food and drinks to pilgrims nearby at the time of the blast. “I can't understand how this suicide bomber reached this point. No one can get in here without going through seven checkpoints,” he said. US forces in Iraq came under an Iraqi mandate on Jan. 1 in step with a pact that will require the withdrawal of the 140,000 US troops by the end of 2011. As the United States reduces its activities in Iraq, local forces are taking greater responsibility for security. Sunday's bomb attack was a reminder of the challenges they face, almost six years after the US-led invasion in 2003. Moussawi said the government had ordered an investigation and a tightening of security surrounding the pilgrimage. In 2004, at the first Ashura pilgrimage after Saddam's fall, militants killed more than 160 Shi'ite pilgrims in coordinated attacks on the Kadhimiya and Kerbala shrines. Hundreds of thousands of Shi'ites will visit the holy city of Kerbala, 80 km (50 miles) southwest of Baghdad this week.