Iraqi police forces have arrested a top al-Qaeda member over the killing of a senior lawmaker in the capital Baghdad last week.

The police say Ahmed Abed Oweiyed -- the deputy commander of Al-Qaeda's military wing in Iraq -- was arrested in the capital on Wednesday following concerted intelligence efforts over the assassination of Harith al-Obaidi.

Police believes Oweiyed is the mastermind behind the attack.

"We received information from one of our sources in Ghazaliyah that the group involved in the assassination were in one house," AFP quoted Brigadier General Noaman Dakhil Jawad, the commander of the police's rapid intervention forces in Baghdad, as saying.

Al-Obaidi -- head of the Iraqi parliament's biggest Sunni Muslim bloc and a human rights advocate -- was shot dead outside a mosque in Al-Yarmuk neighborhood on Friday.

The teenage gunman also killed five others and wounded at least twelve before committing suicide.

The Iraqi lawmaker was killed shortly after he urged Prime Minister Nuri al-Maliki to launch an independent inquiry into reported cases of torture, rape and death in the country's prisons.

His assassination also came less than three weeks ahead of US combat troops' withdrawal from Iraq's urban centers, as part of a security accord between Baghdad and Washington.

Prime Minister Nuri al-Maliki has repeatedly said that the militant attacks are likely to rise in the coming weeks to "undermine confidence in Iraq's own security forces".