* Eight car bombs killed 28 in Baghdad on Sunday
* Al Qaeda says revenge for state repression of Sunnis
* Sectarian attacks mounting since start of year (Adds background, bullet points)
BAGHDAD, Feb 18 (Reuters) - Al Qaeda's Iraqi wing claimed responsibility on Monday for car bomb blasts that killed 28 people in Shi'ite Muslim districts in Baghdad, saying it was taking revenge for perceived state repression of Sunni Muslims.
The al Qaeda affiliate Islamic State of Iraq and other Sunni Islamist groups oppose Prime Minister Nuri al-Maliki's Shi'ite-led government which they say discriminates against the country's Sunni minority.
Once at the heart of the insurgency against U.S. troops in Iraq, al Qaeda now targets mainly Shi'ites and local security forces in an attempt to trigger the kind of widespread sectarian violence that drove the oil producer to the edge of civil war in 2006-2007.
"We say to the Sunnis in Baghdad and elsewhere: The situation in which you are living today is exactly what the mujahideen warned you of years ago. You are walking in a dark tunnel," said the statement posted on an Islamist website on Monday.
At least eight car bombs exploded near shops, restaurants in Baghdad's busy commercial streets on Sunday.
One blast tore off shop fronts in Qaiyara district while another left the remains of a car and its twisted engine littered across a high street in the busy, commercial Karrada district.
Insurgents are stepping up attacks at a time when Maliki is facing two months of protests by thousands of Sunni Muslims in western provinces, who accuse his government of marginalising their sect.
Maliki's power-sharing government includes Shi'ites, Sunnis and ethnic Kurds. The Shi'ite premier has offered concessions to protesters, such as releasing detainees held by security forces and modifying laws Sunnis say are used to target them.
The wave of attacks was the latest sign of a campaign that has escalated since the start of the year and had heightened the risk of wider inter-communal violence in the OPEC country.
Islamic State of Iraq and other Sunni Islamist groups have carried out at least one major assault a month since the last U.S. troops left in December 2011. But since January, more than ten suicide bombers have struck different targets. (Reporting by Ahmed Rasheed; Editing by Patrick Markey and Andrew Heavens)