It added that the coalition issued several warnings before it destroyed two artillery pieces and an anti-aircraft weapon and damaged a tank.
The coalition said it does not seek confrontation with the "Syrian regime or pro-regime forces", but stressed it is ready to defend its troops and partners "if pro-regime forces refuse to vacate the de-confliction zone".
The Tanf outpost, located near the Syrian, Iraq and Jordanian border, has quietly become a flashpoint in the six-year old Syrian conflict in recent weeks.
On May 18, the USA air force struck a convoy of pro-government fighters advancing in the desert near the Tanf border crossing with Iraq.
This Friday, April 28, 2017, still taken from video, shows US forces patrolling on a rural road in the village of Darbasiyah, in northern Syria.
Coalition forces were forced to engage in a similar strike May 18 after pro-regime forces advanced into the de-confliction zone.
The pro-regime, Iranian-backed rebels want to take the border crossing into southern Iraq, but to do that they have to go through at al-Tanf where USA and Jordanian special forces are working with Syrian opposition forces, CBS News national security correspondent David Martin reports.More news: Thad Matta out as basketball coach at Ohio State
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Jihan Sheikh Ahmed, the official spokesperson of the al-Raqqa campaign, told dpa that the forces had entered the neighbourhood of al-Mosheileb on the Syrian city's eastern edge.
The statement warned of the risks of such escalation and its reverberations, urging the US-led coalition to curb such acts. On Tuesday, a convoy entered the 110 km-diameter deconfliction zone, posing a threat to coalition and partner forces, according to CENTCOM.
The United States military is increasing its "combat power" in southern Syria around an American military training camp in al-Tanf, a Syrian town on the border with Iraq, on the Syrian side of Iraq's al-Waleed border crossing.
"This aggression comes once again to stress the supportive role of terrorism by the forces which claim otherwise, and at the time when the Syrian army is making progress against the terrorist group of the Islamic State organization", the army said.
The group, which Defense Secretary James Mattis previously said may be directed by Iran, was within the "deconfliction zone" established by the US and Russian Federation, which extends roughly 34 miles out from At Tanf.
"Within a few days, you will find us at the Iraqi border, and we will achieve a great and historic victory in the history of this crisis - cleansing the entire Badia, liberating the Tanf road. and restoring the vital artery between Iraq and Syria", said one of the soldiers interviewed by the state TV channel in the Badia area.
Pro-Assad Shia militias backed by Iran have historically operated in that area.