Mounting Iraqi violence concerns U.N. Share This: UPI 2/18/2013 3:25:30 PM BAGHDAD, Feb. 18 (UPI) -- The Iraqi division of al-Qaida said Monday it was responsible for a series of attacks that hit Shiite-populated areas last weekend. At least 28 people were killed and another 100 were wounded in attacks last weekend in and around Baghdad. Al-Qaida's Islamic State of Iraq said Monday it carried out the attacks in retaliation for what it said was the repression of Sunni groups, reports Voice of America. Martin Kobler, U.N. special envoy to Iraq, said there's nothing to justify terrorist attacks in Iraq. "All Iraqi leaders have a responsibility to stand up against these atrocious crimes targeting the social fabric of the country," he said in a statement. Iraqi Prime Minister Nouri al-Maliki, a Shiite, has faced mounting frustration from Sunnis. Tensions flared in Iraq after U.S. forces left the country in December 2011. Kobler in January said he was alarmed by the escalation of violence after the offices of political parties in Kirkuk were attacked. Iraq has local elections scheduled in April and national elections in 2014. The International Crisis Group called on Maliki to avoid seeking a third term in office.