At least four people were killed and 11 others injured on Tuesday in two suicide bomb attacks targeting government-backed paramilitary Shia unit in Iraq's Salahudin province, a security source said.A suicide bomber blew himself up at a checkpoint manned by Hashd Shaabi unit in Sulaiman Beg town, Xinhua quoted the source as saying.Minutes later, another blast occurred as the security forces and people gathered at the site, the source said.The attackers followed a familiar tactic by creating an initial explosion to attract people, and then setting off another blast to inflict heavier casualties, he said.The Iraqi army and allied paramilitary units have been battling IS militants to recapture territories in northern and western Iraq that was seized by the militant group since June 2014.A report by the UN Assistance Mission for Iraq said 741 Iraqis were killed and 1,374 injured in acts of terrorism, violence and armed conflicts in April across the country.