Assailants in a vehicle shot Shaikh Faidh Muhammad Amin al-Faidhi as he was leaving a place of worship in Mosul's al-Rifaq district at about 9am (0600 GMT) on Monday.
"The cleric was shot four times, in his chest and abdomen, and died shortly after he was transferred to hospital," said Abd al-Jabbar Muhammad, a doctor at Madinat al-Tib hospital.
The cleric was a member of influential Iraqi Muslim body the Association of Muslim Scholars (AMS), and the brother of the organisation's spokesman in Baghdad, Muhammad Bashar al-Faidhi.
The AMS has called for a boycott of elections planned for 30 January. It says its members have been targeted by US and Iraqi security forces and also by armed fighters trying to fuel sectarian unrest.
The AMS was formed after Saddam Hussein's ousting last year by US-led forces to try and fill a political vacuum among Sunnis. It maintains ties with anti-US Shia groups, such as the movement led by leader Muqtada al-Sadr.
Also in Mosul, four bodies, at least three of them Iraqi soldiers, were found in the past 24 hours by the US military, a US army officer said on Monday.
"We found them at 2300 (2000 GMT on Sunday). They had been dead for at least a couple of hours and their bodies set against the sidewalk, shot in the head and hands tied," Lieutenant Colonel Michael Kurilla said, adding that three of them were confirmed as being Iraqi soldiers.
The bodies were found near the al-Yarmuk roundabout, and brought to 15 the number of Iraqi soldiers thought to have been executed by fighters in Iraq's third largest city over the past two days.
Iraqi police attacked
In a separate development, an Iraqi national guardsman was injured in an attack by armed fighters targeting a joint checkpoint of US forces and Iraqi forces on al-Dhuluaiya bridge south of Tikrit city, sources told Aljazeera.
Also in Tikrit, the purported al-Tawhid wa al-Jihad group distributed leaflets in al-Toz suburb, east of the city, calling on Iraqi national guardsmen and government departments in the area to refrain from going to work.
Iraqi police are often targeted
by armed fighters
Meanwhile, US forces arrested five Iraqi policemen and confiscated their weapons at a checkpoint in Ishaqi district south of Tikrit.
US soldier killed
Separately, an American soldier was killed in an attack in south-western Baghdad, the US military said on Monday.
"A Task Force Baghdad soldier died from wounds sustained in
an attack at about 10pm (1900 GMT) on 21 November in south-western Baghdad," it said in a statement, giving no more details.
Also in Baghdad, a child was killed and four people wounded when a mortar shell struck a residential neighbourhood, police said.
The mortar shell hit the Bab al-Shaikh neighbourhood, killing one child and wounding four people, including a woman, a policeman on the scene said.
Baghdad has been rocked by daily violence, including car bomb, roadside bomb, rocket and mortar attacks mainly aimed at US or Iraqi military targets but which often kill Iraqi civilians.