BAGHDAD , Iraq ( CNN ) -- A man in a wheelchair blew himself up Monday in a northern Iraqi police station , killing three National Police officers , including a commander , police said . Soldiers stand by as pilgrims gather Sunday in Karbala for al-Arbaeen , one of holiest days on the Shiite calendar . The attack also wounded nine officers on the police force , which the Iraqi Interior Ministry operates . The bombing in Samarra raises concern about the recent tactics employed by insurgents in Iraq . Bombs have been placed inside dead animals and hidden in carts . And in recent days , vagrants have been involved in bombings . `` As a sign of desperation , some of those terrorists resorted to some new methods and techniques , '' said Maj. Gen. Qassim Atta , spokesman for Baghdad 's security plan . One of the tactics is the use of remote-controlled `` sticky '' bombs , small enough to tape under vehicles . A high-ranking Samarra police official said the disabled man came to meet with Brig . Gen. Abdul Jabbar Rabei Muttar , deputy commander of security , at the security operations building in Samarra . The pair met last week as well . The man was searched when he entered the building , but police did n't look under his wheelchair seat , where the explosives had been placed . The man , who police say was cogent , detonated the explosives when Muttar approached him . Also Monday , a roadside bomb exploded in the middle of a crowd of Shiite Muslims in Baghdad , killing three people and wounding 15 , an Interior Ministry official said . The strike , in southeastern Baghdad 's Zafaraniya district , is the latest attack against pilgrims trekking to Karbala for al-Arbaeen , one of the holiest days of the Shiite religious calendar . It falls on Wednesday . On Sunday , a suicide bomber in Iskandariya killed at least 45 people and wounded 68 others , and armed militants attacked pilgrims in southern Baghdad , killing three and wounding more than 30 others . Pilgrims traditionally make their way to Karbala on foot as a demonstration of piety , and those who head to the city from Baghdad go through Babil province , where Iskandariya is located . Joint forces have stepped up patrols during the pilgrimage to protect the thousands headed to Karbala . Last year , more than 180 pilgrims were killed in a series of attacks , most during twin suicide bombings in Hilla , Babil province 's capital . Sunday 's attack in Iskandariya , conducted by a bomber wearing an explosive vest , prompted authorities there to replace the police chief , Hilla police said . More National Police officers have been deployed to Babil to ensure the safety of pilgrims heading to Karbala , a police official said . The U.S. Embassy in Baghdad and American-led coalition forces condemned Sunday 's `` barbaric attacks in Baghdad and Iskandariya '' against `` innocent citizens participating in an important religious commemoration . '' Every year , thousands of pilgrims amass in Karbala for al-Arbaeen , which commemorates the end of a 40-day mourning period for Imam Hussein , the grandson of the Prophet Mohammed . Hussein , one of the most revered Shiite martyrs , is buried in Karbala , about 60 miles southwest of Baghdad . Karbala 's main holy site is the gold-domed Imam Hussein Shrine . Other developments . CNN 's Mohammed Tawfeeq contributed to this report .
Iraqi major says attacks show how insurgents are resorting to new methods . Police : No one has been killed in the attack, but a police officer was wounded and is being treated at an area hospital for his injuries. Three people are killed , 15 injured in roadside attack in southeastern Baghdad . Pilgrims on way to Karbala for al-Arbaeen , one of holiest days on Shiite calendar .