At least 116 people were killed and about 300 wounded in bomb and gun attacks on Monday, by far the bloodiest day of violence since U.S. troops withdrew in December. A day earlier 20 were killed in bombings as part of a co-ordinated surge of violence.
"The Ministry of War has mobilized its sons and mujahideen brigades and their military groups in a new blessed foray in the holy month of Ramadan," the ISI statement said.
"Simultaneous and co-ordinated jihadist operations have swept across the country in a spate which stunned the enemy, made him lose his sense and showed the failure of intelligence and security plans which filled the world with noise and bluster."
On Monday insurgents hit targets including Shi'ite areas of Baghdad, the Shi'ite town of Taji to the north and the northern cities of Kirkuk and Mosul, hospital and police sources said.
The ISI often hits Shi'ite targets to try to stir up the type of sectarian violence that drove Iraq to the edge of civil war and killed tens of thousands of people in 2006-2007.
Political tensions have escalated between Iraq's main Shi'ite, Sunni and Kurdish factions since the U.S. withdrawal.