Iraqi officials say a wave of bombings and shootings has killed at least 106 people and wounded more than 200 others across the country.

Insurgents carried out the coordinated attack in at least 15 cities Monday. It was Iraq's bloodiest day since May 10, 2010 when more than 100 people were killed.

The worst attack was in Taji, 20 kilometers north of Baghdad, where nearly 40 people were killed and scores more wounded. A series of explosions at a housing complex was followed by a later blast that killed and wounded a number of police who had arrived at the scene.

Authorities said the attacks Monday included gunmen killing at least 15 Iraqi soldiers at a military base in northeastern Iraq, a series of explosions in the northern city of Kirkuk, as well as a car bombing in Baghdad.

There was no immediate claim of responsibility.

The violence comes after jihadist websites posted a message Saturday, purportedly from the leader of al-Qaida's affiliate in Iraq, saying the group is starting a “new phase.” The audio message from a speaker identified as Abu Bakr al-Baghdadi says the Islamic State of Iraq is planning to attack court officials, and to free prisoners.

In June, the group claimed responsibility for a wave of car bombings that killed 72 people and wounded nearly 260 others.