At least 20 people were killed and 70 others wounded when two suicide bombers on Friday blew themselves up in Iraq's Salahuddin province, officials said.The attack occurred shortly after midnight when a group of gunmen disguised in military uniforms stormed the shrine of Saiyd Mohammed in the town of Balad, 80 km from Baghdad, Xinhua news agency reported.Two suicide bombers detonated explosives with themselves at the shrine, a security source said on condition of anonymity.The gunmen, believed to be members of Islamic State (IS), also held an unknown number of Shiite pilgrims hostages inside the shrine, but the security forces freed the hostages after fierce clash, killing all the attackers, the source said.The battle caused damages to the shrine and set fire to some surrounding buildings, the source added.