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Armed Iraqi Shiite fighters shout slogans during clashes with Islamic State group militants, July 15, 2015, in Saqlawiya, Iraq, 50 km west of Baghdad. Ahmad Al-Rubaye/AFP/Getty Images

In their most significant offensive in northern Iraq in more than five months, Islamic State group militants staged a three-pronged attack Wednesday night north and east of Mosul, American officials said Thursday, the New York Times reported. Each of the coordinated attacks involved 80 to 120 fighters for the group, which is also known as ISIS or ISIL.

American officials estimated that 180 ISIS fighters were killed in airstrikes carried out by American, British and French aircraft. Hundreds more militants might have been killed by peshmerga fighters.

“The last 24 hours are a grim reminder of why we should not underestimate ISIS and how badly the peshmerga need more ground support in addition to continued air support,” said Masrour Barzani, chairman of the Kurdish region’s security council, the New York Times reported.

The attacks took place in Narwan, Bashiqa and Tal Aswad and the ISIS militants used armored bulldozers, trucks with mounted machine guns and vehicles driven by suicide bombers.

“As attacks go, they were pretty significant,” said Brig. Gen. Mark Odom, the senior American officer in northern Iraq, the New York Times reported. The last time a serious attack occurred was on July 6, he said.

Meanwhile, in a private session at the White House, President Barack Obama explained his refusal to redeploy large numbers of troops to the Middle East. He said casualties and costs would compete with the worst of the Iraq War, the New York Times reported Thursday. Obama said the effort could require as much as $10 billion a month and leave as many as 500 troops wounded every month, in addition to those killed.