According to the news item, what happened in the northern city Mosul?

The violence began before dawn, with gunmen in speeding cars killing soldiers and police at checkpoints across Baghdad. The assailants used silencers, a new gangland-style twist to their attacks.
    In the hours that followed, two bombs, also targeting police, exploded in the capital. Other blasts occurred outside the homes of policemen in Fallujah, west of Baghdad. This Fallujah resident said one of the houses destroyed belonged to a policeman killed two years ago. He says members of the family have been drubbed from the rabble and asked "What did they do?"
    In the northern city Mosul, a suicide bomber exploded a car near a checkpoint guarded by national and Kurdish forces. Two blasts also rocked Suwayra, southeast of Baghdad. In the deadliest attack, two car bombs struck workers in Hilla, in central Iraq.
    While there was no immediate claim of responsibility, suspicion quickly fell on al-Qaida in Iraq as well as Sunni militants. Iraqi and US officials, in recent weeks, had announced several arrests and killings of top al-Qaida leaders. Authorities predicted the actions would weaken the local off-shoot of the terror network, arguing that support for the group had waned and replacing the leadership would be difficult.