What is Tower 22, site of the attack on US troops in Jordan?

Three US troops were killed and dozens wounded after a drone hit a military outpost in Jordan known as Tower 22.

Here is what is known about the base:

Location

Tower 22 holds a strategically important location in Jordan, at the most northeastern point where the country's borders meet Syria and Iraq.

Purpose

Little is publicly known about the base. But it includes logistics support and there are 350 US Army and Air Force troops at the base.

Tower 22 is near Al Tanf garrison, which is located across the border in Syria, and which houses a small number of US troops. Tanf had been key in the fight against Islamic State and has assumed a role as part of a US strategy to contain Iran's military build-up in eastern Syria.

Tower 22 is located close enough to US troops at Tanf that it could potentially help support them, while also potentially countering Iran-backed militants in the area and allowing troops to keep an eye on remnants of Islamic State in the region.

US troops in Jordan

Jordan's army is one of the largest recipients of Washington's foreign military financing.

The kingdom has hundreds of US trainers and is one of the few regional allies that hold extensive exercises with US troops throughout the year.

Since the start of the Syrian conflict in 2011, Washington has spent hundreds of millions of dollars to help Amman set up an elaborate surveillance system known as the Border Security Programme to stem infiltration by militants from Syria and Iraq.

Many unknowns

It is unclear what type of weapons are kept at the base, air defences used, and what exactly went wrong.

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