A series of bomb attacks has struck northern Iraq, highlighting instability in a region that U.S. military officials say is one of the last Sunni insurgent strongholds in the country.

In the worst attack, at least 40 people were reported killed in a car bomb attack in the Diyala province capital of Baqouba. Iraqi police officials said at least 70 others were wounded in the attack, which hit outside the provincial government offices in the city.

The Associated Press reported it was the deadliest bombing in Iraq since March 6 when a twin bombing killed 68 people in a crowded shopping district in the central Baghdad district of Karradah.

Diyala province has been an area of continuing violence; U.S. military officials have said they believe Sunni insurgents were pushed there after offensives in Anbar and Baghdad provinces.

Three buses were destroyed and 10 local shops were damaged, the military said.

“Although attacks such as today’s event are tragic, it is not indicative of the overall security situation in Baquba,” Maj. Mike Garcia, spokesman for coalition forces in Diyala province, was quoted as saying. “This is the first suicide attack inside Baquba in almost 90 days, and the overall violence in the city has decreased by 80 percent since June.”

Three car bomb attacks also struck in Mosul on Monday, officials said. No military or civilian deaths were reported in the incidents, but several Iraqi soldiers and civilians were wounded.

“The first attack was against a Coalition forces convoy in the northwest side of the city. No Coalition force Soldiers were injured, however five Iraqi citizens were injured in the attack. Additionally, a Coalition vehicle was damaged by the blast,” a U.S. military statement issued Tuesday read.

“The other two car bombs were part of a complex attack with small arms fire in the southwest side of the city. The attack injured an Iraqi soldier and damaged a store and cars in the area.”

Earlier this year, Iraqi prime minister Nouri al-Maliki promised a “decisive” battle against al-Qaida in Iraq in Mosul. U.S. officials then said the effort would be a drawn-out process.

“Regardless of the target, these attacks mostly injure innocent Iraqis and their protectors,” said Maj. Peggy Kageleiry, a U.S. military spokeswoman in northern Iraq. “The Iraqi Security Forces continue to fight these insurgents with their Coalition partners with increasing skill and confidence.”

A separate attack on Monday struck a wake for an Iraqi soldier in Tal Afar. An attacker using a suicide bomb vest killed three and wounded 35 others, the U.S. military said.

“The attack occurred at a house as family and friends attended a wake for an Iraqi army soldier killed two days prior to the attack,” officials said. “All those injured from this attack have been taken to a nearby hospital for treatment.”