Your trusted source

A senior U.S. military official says the operation to retake Iraq’s second largest city from Islamic State of Iraq and Syria (ISIS) militants will likely begin in April or May and will involve about 12 Iraqi brigades, or between 20,000 and 25,000 troops, IraqiNews.com reports.

The initial attack force will consist of about 10,000 Iraqi troops, CBS News correspondent David Martin reports. The rest of the force would be held in reserve and include Kurdish fighters along with Iraqi soldiers and special operations forces. U.S. military advisers will give training to all of the troops in the attack force.

The official from U.S. Central Command says five Iraqi Army brigades will soon go through coalition training in Iraq. The official says there are about 1,000 to 2,000 ISIS insurgents in the city of Mosul. The group overtook the northern Iraqi city last June. Military leaders have been talking about retaking the city for some time.

Mosul is of strategic importance. The city and surrounding Ninevah province are a major export route for Iraqi oil and a gateway to Syria. It was taken by militants last June.

April or May was chosen as a date to start so the fighting could end before the worst of Iraq’s summer heat comes. If Iraqi forces are not ready by April or May, the operation could be delayed, the official says, speaking anonymously because he was not authorized to discuss the operation publicly.

No decision has been made yet on whether U.S. military advisers will accompany Iraqi troops to call in airstrikes against ISIS targets.