JERUSALEM (AP) — A little-discussed United States military desert outpost in the far reaches of northeastern Jordan has become the focus of international attention after a drone attack killed three American troops and injured at least 34 others there.

The base, known as Tower 22, sits near the demilitarized zone on the border between Jordan and Syria along a sandy, bulldozed berm marking the DMZ’s southern edge. The Iraqi border is only 10 kilometers (6 miles) away.

The area is known as Rukban, a vast arid region that once saw a refugee camp spring up on the Syrian side over the rise of the Islamic State group’s so-called caliphate in 2014.

At its height, over 100,000 people lived there, blocked by Jordan from coming across into the kingdom at the time over concerns about infiltration by the extremist group. Those concerns grew out of a 2016 car bomb attack there that killed seven Jordanian border guards

The camp has dwindled in the time since to some 7,500 people because of a lack of supplies reaching there, according to United Nations estimates.

The base began as a Jordanian outpost watching the border, then saw an increased U.S. presence there after American forces entered Syria in late 2015. The small installation includes U.S. engineering, aviation, logistics and security troops with about 350 U.S. Army and Air Force personnel deployed there.

The base’s location offers a site for American forces to infiltrate and quietly leave Syria. A small American garrison at al-Tanf in Syria is just 20 kilometers (12 miles) north of Tower 22. That base is along a Syrian highway leading into Iraq and ultimately Mosul, once a prominent base of the Islamic State group. It’s also a potential weapons shipment route over the road for Iran.

COLUMBIA, S.C. (AP) — President Joe Biden said Sunday that the U.S. “shall respond” after three American troops were killed and dozens more were injured in an overnight drone strike in northeast Jordan near the Syrian border. Biden blamed Iran-backed militias for the first U.S. fatalities after months of strikes by such groups against American forces across the Middle East since the start of the Israel-Hamas war.

Biden, who was traveling in South Carolina, asked for a moment of silence during an appearance at a Baptist church’s banquet hall.

“We had a tough day last night in the Middle East. We lost three brave souls in an attack on one of our bases,” he said. After the moment of silence, Biden added, “and we shall respond.”

With an increasing risk of military escalation in the region, U.S. officials were working to conclusively identify the precise group responsible for the attack, but they have assessed that one of several Iranian-backed groups was behind it.

China on Tuesday warned against a "cycle of retaliation" in the Middle East after the United States vowed to respond to a drone attack on a base in Jordan that killed three American troops, which it blamed on Iran-backed militants.

The casualties -- the first US military deaths in an attack in the region since the Israel-Hamas war began -- raised fears of an escalating conflict, as fighting rages in Gaza.

Iran has said it had nothing to do with the attack and denied US accusations it supported militant groups behind Sunday's strike on the remote frontier base in Jordan's northeast, near the borders with Iraq and Syria.

Beijing said Tuesday it had "noted reports of casualties caused by the attack on a US military base".

"We have also noted that Iran stated that it had nothing to do with the attack," foreign ministry spokesperson Wang Wenbin said.

"We hope that all relevant parties will remain calm and restrained... in order to avoid falling into a vicious cycle of retaliation and prevent further escalation of regional tension," he added.