Saleh al-Mutlaq, an outspoken member of parliament whose Iraqi National Dialogue group is part of the US.-backed political process, said US forces had targeted his office, killing two security guards and wounding two more.
Speaking to Reuters by telephone from outside Iraq, Mutlaq also said a family of four, including two children, were killed in an adjacent building during the raid today.
He said the raid was a provocation and said the US-backed government should be targeting Shi'ite militias blamed for operating death squads rather than his political party.
''Coalition forces killed six terrorists and detained one suspected terrorist during a fierce firefight Monday morning in Baghdad,'' a US statement said.
''Intelligence reports indicated the targeted location was used as a possible safe house for al Qaeda in Iraq terrorists to conduct operational planning,'' it said, adding US forces were fired on from several buildings nearby and that two buildings caught fire because of the intense firefight.
''One of the buildings from which Coalition Forces received heavy enemy fire, including grenade launches, was later identified as belonging to Dr Saleh al-Mutlaq,'' it said.
Photographs of the scene showed the exterior wall surrounding the building reduced to a pile of rubble and the office building damaged with windows broken and damage from gunfire. There was a pool of blood outside.
The ubiquity of armed guards on premises around Baghdad and the frequency of illegal attacks by gunmen in uniform means that misunderstandings do at times lead to clashes between legitimate security guards and official government forces.
Asked about reports of civilian casualties, a U.S. military spokesman said by email: ''We are not aware of any civilians being injured or killed in this morning's raid. Coalition Forces returned fire against armed terrorists only. The terrorists killed were armed males firing at Coalition Forces.'' Mutlaq's group is one of several Sunni Arab parties in Prime Minister Nuri al-Maliki's national unity government, which also includes majority Shi'ites and ethnic Kurds.
Mutlaq has warned brutal US tactics are radicalising Sunni Arabs and swelling the ranks of al Qaeda and has urged Maliki's government to focus on cracking down on Shi'ite militias blamed by Washington and Sunni Arabs for operating death squads.
''I don't know why they are targeting us and not the militias.
We don't have militias, we are the only front that doesn't have a militia,'' Mutlaq said. ''They want to involve us in a war and to stop the political process.'' Reuters MS GC1852