It's time for the United States to hold Iran accountable.

New efforts by Iranian-backed militias to control supply lines in southern Syria highlight an alarming trend in the war-torn region: Militias and their foreign backers are accelerating their rivalry for power as the U.S.-led coalition shrinks the Islamic State’s territory.

“You can see everyone maneuvering frenetically,” said Michael Knights, an analyst at the Washington Institute for Near East Policy.

The problem surfaced in recent weeks when Iranian-backed militias maneuvered close to a U.S. outpost in southern Syria. The outpost at al-Tanf is a base for several hundred coalition advisers and the local forces they are supporting.

Last week, U.S.-led coalition aircraft struck the militias for a third time to warn them away from U.S. forces. An American warplane also shot down an Iranian-built armed drone operating in the same area after it fired at U.S. advisers and their partner forces.

Analysts say the primary objective of the Iranian forces is not to threaten U.S. forces. Instead, the militias are defending Iran’s supply routes to Lebanon that go through Iraq and southern Syria.

The Islamic State, or ISIS, "was always destined to be defeated, and now the U.S. and its allies have to contend with an emboldened, belligerent, and more powerful Iran, which has cultivated more proxies than ever,” said Ali Khedery, a former special assistant to five U.S. ambassadors in Iraq.

The Pentagon sees the Iranian-backed militias as a potential distraction from the fight against ISIS.

“The coalition calls on all parties in southern Syria to focus their efforts on the defeat of ISIS, which is our common enemy and the greatest threat to the region and the rest of the world,” said Col. Ryan Dillon, a Pentagon spokesman.

Analysts say the array of militias and foreign powers in the region have differing objectives, which are coming to the forefront as ISIS is pushed out of its strongholds in Iraq and Syria, leaving a power vacuum.

For countries such as Iran and Russia, defeating ISIS was never the main objective. Both countries are the principle backers of Syrian President Bashar Assad.

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