What to know about Tower 22, the US base in Jordan struck in deadly drone attack

Sunday's deadly drone attack on a small U.S. base in Jordan known as Tower 22 has highlighted a little-known mission in the barren desert area just one mile south of the country's border with Syria.

The strike, which the U.S. has blamed on Iran-backed militants, has also sparked public questions about why it is that U.S. troops have been stationed in this remote location.

"That specific mission ... has been in effect since 2014, when the counter-ISIS campaign began in earnest," said retired Gen. Robert Abrams, a former commander of U.S. Forces Korea and an ABC News contributor, referring to U.S. efforts to dismantle the Islamic State group.

"It started as a tiny little postage stamp with probably 30 people providing support to U.S. special operations forces and our partners operating and beginning to conduct operations against ISIS in Syria," Abrams added.

Tower 22, in northeastern Jordan, has "since grown to be able to support expanding missions and conducting operations for the last 10 years," Abrams said of the post that has now become a major logistical hub for the 900 U.S. troops still in Syria on a mission to prevent a resurgence by Islamic State fighters.

Jordan does not typically publicly acknowledge the presence of U.S. military personnel at bases within its borders, but in the wake of the attack on Sunday, officials there said American troops had been stationed to help Jordan with border security.

U.S. Central Command also disclosed new details about the little-known base.

"There are approximately 350 U.S. Army and Air Force personnel deployed to the base, conducting a number of key support functions, including support to the coalition for the lasting defeat of ISIS," read a CENTCOM statement.

Close-up satellite images show U.S. military helicopters and buildings at Tower 22, not far from where Jordan abuts Syria and Iraq, and zoomed-out satellite pictures show that the base is only about 15 miles away from the Al-Tanf U.S. military base in Syria that is strategically located on a major highway leading to the Syrian capital of Damascus.

About 100 U.S. troops are stationed at Al-Tanf, hundreds of miles away from other U.S. troops in Syria, in the northeastern and eastern parts of the country.

While the forces at Al-Tanf also have a counter-terrorism mission, their presence on the highway to Damascus is also intended to counter Iran's weapons smuggling to Hezbollah in Lebanon.

Tower 22's close proximity to Al-Tanf means it is able to provide logistical and air support for the smaller, more isolated base in Syria. And its growth over the years means it now houses more than three times as many U.S. troops as those located at Al-Tanf -- and is about a third of the size of the entire U.S. contingent in Syria.

According to the Pentagon, the one-way attack drone that struck the base early on Sunday ended up targeting some of the containers used as living quarters on the base.

The drone was probably able to slip past defenses at Tower 22 because American personnel mistook it for one of their own returning from a surveillance mission, two U.S. officials said on Monday.

A Pentagon spokesperson said Monday that the drone strike was the first time that the base had been targeted in the more than 165 drone and rocket attacks on U.S. forces in Iraq and Syria since mid-October, which the U.S. says have been conducted by Iranian-backed militia groups in opposition to Israel's campaign against Hamas in Gaza.

Iran has denied involvement in Sunday's attack with a spokesman saying, in part, "War is not a solution."

ABC News' Anne Flaherty, Somayeh Malekian and Nadine Shubailat contributed to this report.