Iraqis gather at the site of a car bombing in Baghdad. Five car bombs detonated in the Iraqi capital on Monday, killing 64 people, according to a security official. (Ali Abbas/EPA)

Five car bombs detonated in the Iraqi capital on Monday, marking a bloody start to the year as Iraq attempts to squeeze Islamic State militants from their last remaining territory in the country.

Sixty-four people were killed in the attacks, according to a security official from Baghdad Operations Command, who spoke on the condition of anonymity because he was not authorized to release the death toll.

The worst bombing killed 30 people in a market in the Sadr City area of Baghdad, a largely Shiite neighborhood that is a regular target for the Islamic State. The attacker was driving an explosives-laden pickup truck and pretended to be recruiting day laborers, Prime Minister Haider al-Abadi said at a news conference. He waited for them to crowd around the vehicle and then set off the bomb.

The Islamic State asserted responsibility via the affiliated Amaq news agency.

Iraqi forces are 2½ months into an offensive to oust the group from the northern city of Mosul, the largest population center that the group controls. They have slowly clawed back territory, but the militants have not ceded ground easily, inflicting heavy casualties.

Monday’s multiple bombings appeared designed to shake confidence in the capital, and they followed a twin bombing in Baghdad on New Year’s Eve that killed 28 people.

The U.S. State Department condemned the attacks “in the strongest possible terms,” saying in a statement that “these vicious acts of mass murder are a sobering reminder of the need to continue coalition operations” against the Islamic State.

A hospital in the Sadr City area also was struck Monday, killing 27. Another car bomb detonated near al-Kindi hospital in central Baghdad, killing one. Two other car bombs killed six people, the security official said.

Meanwhile, Islamic State militants launched an attack on the main road from Baghdad to Mosul, a key military supply route. The road was reopened later in the day, officials said.

Abadi had pledged to regain control of Mosul by the end of the year but now says it will take three more months to rid the country of Islamic State militants. Only about a quarter of the city is back under government control, and the presence of more than 1 million civilians is complicating the effort.

Gunmen also attacked a police station Monday in Samarra, north of Baghdad, where clashes continued late into the night and a curfew was imposed.