Iraqi soldiers found 17 decomposed bodies early Wednesday north of the Iraqi capital, an Iraqi army officer said.
The mass grave was discovered in an area of brush near a school in Hashimiyat, an area west of Baqouba, said Col. Ihsan al-Shimari.
Baqouba, some 60 kilometers (35 miles) northeast of Baghdad, is the provincial capital of Diyala - a troubled area where al-Qaida in Iraq is believed to have a strong presence.
Many of the bodies were handcuffed and blindfolded, al-Shimari said.
He said he believed the bodies were from passengers kidnapped at fake checkpoints on a nearby road leading to Baqouba.
There were no identification cards on the bodies, and Iraqi investigators were working to identify the victims, al-Shimari said.
Based on the degree of decomposition, al-Shimari said he believed 13 of the corpses had been there more than three months. The remaining four appeared to have been killed a few days ago, he said.
The discovery came a day after the U.S. military announced that another mass grave had been found in Iraq's western Anbar province. Iraqi soldiers found 22 bodies in the Lake Tharthar area on Saturday during a joint operation with U.S. forces, the military said in a statement.
It was the second mass grave discovered in that area in less than a month.
Al-Shimari said he believed more graves would be uncovered soon, because U.S. and Iraqi security forces were for the first time searching some areas that were previously too violent to enter.
Iraq has seen a sharp drop in bombings, shootings and other violence in recent months, since a 30,000-strong U.S. force buildup. The downtown has been especially pronounced in Baghdad and its surrounding belts - Diyala among them.
"This was a stronghold for al-Qaida, and security forces could not reach it in the past. But now the situation is better and our troops can enter," al-Shimari said.
He said the main road through the Hashimiyat area was previously dubbed the "road of death," after dozens of people were kidnapped there.