Gunmen in Iraq have shot to death a Shia politician running for parliament in upcoming elections in April, one of seven people killed in attacks across the country, officials have said.

Hamza al-Shimmari, who was on the list of the Ahrar party, which is loyal to Shia cleric Muqtada al-Sadr, was killed in a drive-by shooting in Baghdad's western Ghazaliyah neighbourhood, police officials told the AP news agency.

The attack came as the government fought armed groups for control of mainly Sunni areas to the west of the capital in a test of the Shia-led government's ability to maintain security in the country.

In other violence on Friday, a car bomb killed four people and wounded 28 on a commercial street in the northern town of Tuz Khormato, according to the mayor, Shalal Abdoul.

Tuz Khormato, a frequent flashpoint for violence, sits in a band of territory contested by Arabs, Kurds and Turkomen about 200km north of Baghdad.

Meanwhile, in the northern city of Mosul, gunmen shot and killed two members of the Shabak minority in a drive-by shooting, said police and hospital officials.

The Shabak are small ethnic minority, many of whose members follow an offshoot of Islam. Most live in villages east of Mosul, the provincial capital of the ethnically mixed Ninevah province that is predominantly Sunni.

Violence has escalated in Iraq over the past year in relentless, near-daily waves of attacks, bombings and shootings.

On Thursday, a string of car bombs hit commercial areas in Baghdad, killing at least 13 people. On Wednesday, 34 people were killed in multiple explosions, mainly in the heart of the capital.

Last year, the country saw the highest death toll since the worst of the country's sectarian bloodletting began to subside in 2007, according to United Nations figures. The UN said violence killed 8,868 last year in Iraq.

Source: Agencies