Ahmed Abdulghafur al-Samarrai, head of the Umm al-Qura mosque that was targeted and one of the founders of an anti-Qaeda militia force comprised of Sunni tribesmen in Baghdad, pointed the finger at the militant group in the aftermath of the attack.
"I am sure Al-Qaeda was behind this attack," Samarrai told al-Sharqiyah television. "We will continue our fight against those criminals and unbelievers. They tried to drag the country into sectarian war before."
Samarrai said he had seen the attacker before at the mosque, describing him as a regular visitor and adding: "That is why it was so easy for him to enter the mosque."
The suicide bomber apparently walked up to a crowd as Samarrai was giving a speech and detonated his explosives.
Among the dead were Khaled al-Fahdawi, an MP from western Anbar province allied with the Sunni-backed Iraqiya bloc, the interior ministry official said. Elderly men and children were also among the casualties.
The Umm al-Qura mosque, located in the Ghazaliyah neighbourhood, is the main headquarters of the Sunni Endowment, which is responsible for maintaining Sunni Muslim religious sites across Baghdad.
Samarrai is known for his sermons against violent extremism. He was one of the founders of the Sahwa, or Awakening Councils, movement in the mostly Sunni north Baghdad neighbourhood of Adhamiyah.
The Sahwa are comprised of Sunni tribesmen who joined forces with the US military against Al-Qaeda from late 2006, helping turn the tide of the insurgency. As a result, Sahwa fighters are despised by Al-Qaeda insurgents, and Samarrai has received several threats against his life.
A car bomb and four roadside blasts in other areas of the capital killed one person and wounded 20 others earlier Sunday, according to the interior ministry official.
Meanwhile, in the restive central province of Diyala, insurgents in military uniforms killed three people in a car at a fake checkpoint they SET up west of the ethnically mixed provincial capital of Baquba, an Iraqi army colonel in Diyala's security command centre said.
In another incident in Diyala, two policemen were killed when gunmen opened fire at their checkpoint in Al-Saadiyah town, the colonel said.
And in the main northern city of Mosul, a magnetic "sticky bomb" attached to a police car in the centre of the city killed a policeman and wounded four others, according to local police.
Two policemen were also wounded when explosives attached to a motorcycle blew up near a petrol station in the town of Tuz Khurmatu, 175 kilometres (110 miles) north of the capital.
Sunday's violence comes after Al-Qaeda's front group in Iraq threatened a campaign of 100 attacks, starting in mid-August, to avenge the death of Osama bin Laden in a US special forces raid in Pakistan in May.
Violence is down across Iraq from its peak in 2006 and 2007, but attacks remain common. A total of 259 people were killed in violence in Iraq in July, according to official figures, the second-highest figure in 2011.