Updated

Gunmen wearing military uniforms pulled seven people from a Sunni mosque south of Baghdad and then shot and killed them execution-style, officials said Tuesday, raising the death toll to 70 in Iraq's deadliest day this year.

The killings late Monday came at the end of a day that saw a wave of crushing violence sweep across Iraq, from the northern city of Mosul to the Shiite heartland — including suicide bombings, roadside bombs and shootings. The violence was reminiscent of the bloodletting that used to plague Iraq daily a few years ago and a stark warning that Al Qaeda in Iraq is still a force to be reckoned with.

The fact that militants were able to pull off such a wave of violence is especially disturbing considering that U.S. forces are scheduled to leave Iraq at the end of this year, leaving the country's security in the hands of still-struggling Iraqi security forces.

Iraqi officials announced earlier this month that they would discuss with the U.S. having a small group of trainers in the country past Dec. 31 but no deal has been finalized.

In the execution-style attack late Monday, the gunmen walked into a Sunni mosque in the town of Youssifiyah during evening prayers, took the seven men outside and shot them, said officials with the Ministry of Interior and the town hospital.

The men were all members of a militia created during the height of the sectarian conflict of Sunnis who used to be aligned with Al Qaeda but later turned on them.

Youssifiyah is about 12 miles south of Baghdad and used to be one of the country's most violent regions, nicknamed the Triangle of Death. It's a Sunni-dominated area that is also home to many Shiite families. Sunni militants used to find easy hiding places among the region's date palm groves.

After the killings, the gunmen shouted they were fighters from the Islamic State of Iraq, a front group for Al Qaeda in Iraq.

The officials spoke on condition of anonymity because they were not authorized to speak to the media.

No group has claimed responsibility for Monday's string of attacks that targeted half of the country's provinces.

But few other terror groups have the organizational skills to carry out such a sophisticated and wide-ranging series of attacks. The use of suicide bombers and the fact that many of the targets were Shiite civilians and Iraqi security forces also indicated that Al Qaeda in Iraq was responsible.

The worst of Monday's violence was in Kut, a Shiite city southeast of Baghdad, where 35 people were killed when two explosions went off in an outdoor market.

A little over a year ago, U.S. and Iraqi officials said the deaths of Al Qaeda in Iraq's two top leaders in a raid had dealt a severe blow to the organization. The group has suffered from a drop in funding and just last week was calling on former members to come back to the fold, a sign of the group's diminished status.

But time and again, Al Qaeda in Iraq has shown an ability to resurrect itself.