The Pentagon said the drone aircraft was similar in size to an MQ-1 Predator, which has a wingspan of 55 feet and weighs more than 1,000 pounds. The base has "become a front-line outpost in the USA containment of regional power Iran, whose allies are advancing on the garrison from two directions", the Christian Science Monitor explained this week.
A military alliance fighting in support of President Bashar al-Assad said on Wednesday it could hit United States positions in Syria, warning that its "self-restraint" over USA air strikes on government forces would end if Washington crossed "red lines".
The Pentagon is not sure Iranian military piloted the aircraft. "We do not see it as a warning shot".
Another U.S. official said the munition landed a few hundred meters from coalition forces and it failed to explode.
Earlier on Thursday, the US-led coalition fighting Daesh terror group (banned in Russia) conducted the third strike against pro-Syrian government forces within a deconfliction zone near At Tanf.
Brett McGurk, the U.S. envoy to the worldwide coalition against Islamic State, said the air strike on Tuesday was meant to defend American forces.
The SDF spokesman Talal Silo told Reuters the battle started on Monday and the fighting would be fierce "because Daesh (Islamic State) will die to defend their so-called capital".
A USA aircraft shot down an unidentified drone deemed hostile toward coalition forces in At Tanf, Syria, a spokesman for Operation Inherent Resolve said Thursday.
On June 8, the coalition said that a pro-Syrian government drone was allegedly used in an attempted attack on the coalition forces to the east from the deconfliction zone. "I do not know the rules of engagement in effect for U.S. ground forces, but an Iranian-Hezbollah assault on Tanf would, I think, be quite reckless and not likely to succeed".
The area is seen as crucial to Assad's Iranian allies and could open an overland supply route from Tehran to Iraq, Syria and Lebanon - the "Shi'ite crescent" of Iranian influence that is a major concern to US-allies in the region. It was a matter of who will reach the Iraqi-Syrian border first, he added. The threat was issued through Hezbollah's military media arm, and included footage of what it said was an Iranian drone tailing an American drone over eastern Syria.
The U.S. military does not speak with the Syrian government.
A downed Israeli military drown shot down in Syria.
The official statement said that the vehicles did not stop despite the show of force and warning shots. The coalition then carried out the airstrike. That convoy, roughly 18 miles from the USA outpost, came to halt.
Viktor Ozerov, the chairman of the Defense and Security Committee of the Federation Council, the upper house of the Russian parliament, said such strikes empower militants.
But CentCom stressed the coalition does not seek to fight Syrian regime forces, nor the Russian and pro-regime forces partnered with them.
The incident happened near the al-Tanf border crossing, between Syria and Iraq, which has become a new flashpoint in the conflict.
Although the Hashd is in a reluctant alliance with the coalition against Islamic State, the USA views these factions as little more than Iranian proxies.
Last week, the coalition said that a relatively "small element" of pro-regime forces continued to hold their position inside the "de-confliction" zone surrounding the coalition training base. Daesh is a pejorative Arabic acronym for Islamic State.
Iranian officials dismissed those claims, saying there was no need for such a geographic link.