Samarrai was also in charge of security at the Adhamiya headquarters of the Sunni Endowment, an institution that runs Sunni mosques and religious offices in Iraq.
The Endowment said the attack was part of "a conspiracy against this country, the blood of which continues to flow".
Other blasts in Baghdad killed five people, including a bomb hidden in a market cart that killed four in the central Karrada district and a pair of roadside bombs that killed a civilian and wounded two policemen in southern Jadiriya district.
Police said they found five bodies of men handcuffed, blindfolded and shot in the head in volatile Diyala province, and gunmen killed a member of a neighbourhood patrol working as a carpenter inside his shop in Samarra.
TARGETS
The neighbourhood volunteers have been increasingly targeted in recent weeks by al Qaeda Sunni Arab militants, who have been driven out of most of the territory they once controlled in Iraq but have continued to launch suicide bombings.
Before the new year al Qaeda leader Osama bin Laden, who is not thought to have direct control over the Iraqi militants that use his organisation's name, vowed to strike the volunteers, who are funded by U.S. forces.
U.S. commanders say attacks on the volunteers are a sign that al Qaeda fears the programme, which has sprouted in Sunni Arab areas where al Qaeda militants ruled the streets until local tribes turned on them in 2006 and 2007.
Adhamiya was one of the militants' main strongholds in Baghdad and one of the deadliest areas for U.S. forces in the capital until mid-2007. It is now a quiet area where shops have reopened and refugees have begun returning.
Although overall levels of violence fell sharply throughout the second half of 2007, U.S. commanders say the Sunni Arab militants remain determined to launch "spectacular" attacks using suicide bombers to kill large numbers of people.
