As many as 100,000 Iranian-backed Shiite militia are now fighting on the ground in Iraq, according to U.S. military officials — raising concerns that should the Islamic State be defeated, it may only be replaced by another anti-American force that fuels further sectarian violence in the region.

The ranks have swelled inside a network of Shiite militias known as the Popular Mobilization Forces. Since the rise of Sunni-dominated ISIS fighters inside Iraq more than two years ago, the Shiite forces have grown to 100,000 fighters, Col. Chris Garver, a Baghdad-based U.S. military spokesman, confirmed in an email to Fox News. The fighters are mostly Iraqis.

Garver said not all the Shia militias in Iraq are backed by Iran, adding: “The [Iranian-backed] Shia militia are usually identified at around 80,000.”

According to some experts, this still is an alarmingly high number.

“The effect of the Obama administration’s policy has been to replace American boots on the ground with the Iranian’s. As Iran advances, one anti-American actor is being replaced with another,” Thomas Joscelyn, a senior fellow at the Foundation for Defense of Democracies, said in a recent phone interview.

Garver said other Popular Mobilization fighters also consist of Sunni tribal fighters from Anbar and Nineveh provinces in Iraq.

Read More: Fox News

Featured Image – fighters raising flag of Iraq and Popular Mobilization Forces – Wikimedia Commons