Iraqi Prime Minister Nuri al-Maliki vowed on Thursday to capture the assassins of an anti-American Shiite MP, the first lawmaker to be killed in 18 months, and ordered a top-level investigation.

Maliki said he appointed a panel headed by Interior Minister Jawad Bolani to probe the assassination of Saleh al-Ogayly, 41, in Baghdad's Sadr City district, a Shiite stronghold.

The Sadrist MP became the first Iraqi legislator to be killed since the April 12, 2007 suicide bombing of the national parliament, where one lawmaker and seven others died.

The assassination was strongly condemned by US ambassador Ryan Crocker and General Raymond Odierno, the commander of US forces in Iraq.

The latest bombing marked a spike in violence at a time when US and Iraqi officials are saying bloodshed is at a four-year low.

Ogayly was among eight people killed on Thursday in fresh attacks in and around Baghdad.

Ogayly, a father of five children, was a member of the parliamentary group of radical anti-US cleric Moqtada al-Sadr.

Sadrists have 28 members in the 275 parliament and are a key opposition.

In another roadside bomb attack just north of Baghdad, an Iraqi Sunni militia leader working with US forces was killed along with two of his children and a nephew, security officials said.

Abbas Khudair, who heads a Sahwa, or Awakening group, that is paid by American forces, was targeted as he drove with his family in the Al-Uthaim area in Baquba, the capital of the restive Diyala province, they said.