US soldiers in Baghdad captured an Iraqi arms dealer and "assassination squad" leader responsible for trafficking Shi'ite extremists in and out of neighboring Iran for training, the military said Sunday. The arrest reinforced long-standing US allegations that Iran arms, trains and funds Shi'ite Muslim militiamen inside Iraq - charges that Teheran denies. It also coincided with a two-day visit to Iran by Iraqi Prime Minister Nouri al-Maliki, his second such trip in a year. The Iraqi prime minister, himself a Shi'ite, is struggling to keep Washington happy while reassuring Iran, the largest Shi'ite nation, that a proposed US-Iraqi security agreement would not make his country an American launching pad for attacks on Iran. The US arrest campaign against Shi'ite militiamen with alleged ties to Iran was likely to be on the agenda for al-Maliki's talks with Iranian officials. US soldiers, acting on intelligence from other Shi'ite militiamen already in custody, captured the Basra-based "special groups" leader late Saturday at a hideout in eastern Baghdad, according to a military statement. "The wanted man is alleged to be a commander of an assassination squad in Basra, an arms dealer with connections to Iran and a document counterfeiter," the statement said. He also arranges transportation of criminals into Iran for training, and then back into Iraq, it said. One of the leader's aides was also arrested without incident. The US military uses the term "special groups" to describe Shi'ite fighters defying a cease-fire order from anti-American cleric Muqtada al-Sadr, whose militiamen fought American and Iraqi forces for seven weeks until a May truce. Meanwhile, the military said in another statement that it captured six more suspected Sunni extremists Sunday in the northern city of Mosul, including an alleged al-Qaida in Iraq leader and another man who is a wiring expert in charge of a bombing cell there. Two women were injured when American soldiers "breached the door of a target building" during the arrest raid, the statement said. Both were treated at the scene and then transported to an Iraqi hospital, it said. Mosul is believed to be one of the last urban strongholds of al-Qaida in Iraq, and US and Iraqi forces have battled with militants there in recent months. Violence continued Sunday in Baghdad, where four new police recruits were killed in an attack on the National Police headquarters on the city's west side, where a blast went off near a gate where recruits were gathering, police said. Another 22 people were wounded in the attack. Police gave conflicting reports about whether the attack used mortars or a roadside bomb. Also, a mortar shell fell near the Defense Ministry building in the Green Zone midmorning, killing one employee and wounding five others, police said. Mortar and rocket attacks were once a daily occurrence in the US-guarded diplomatic zone in central Baghdad, but have fallen off in recent weeks.