State news agency SANA, citing a military source, said that “army units in cooperation with allies managed to arrive at the border … with Iraq” on Friday, and “set up positions in an area northeast of At-Tanf”.
Forces from a US-led coalition fighting ISIL in Syria and Iraq are using a garrison in Al-Tanf to stage attacks against the armed group and train Syrian rebels to fight them.
The SANA report said the advance came after “the last” ISIL fighters in the area “were eliminated”.
The UK-based Syrian Observatory for Human Rights had earlier said that dozens of pro-government forces had arrived at the point on the Syria-Iraq border around 70km north of Al-Tanf.
“What you’re seeing now … is the cutting off of access of coalition-led efforts to push north,” Al Jazeera’s Stefanie Dekker, reporting from Gaziantep on the Turkish-Syrian border, said.
“Why this is important is because up from there is Abu Kamal, a border crossing that ISIL controls on both sides [between] Syria and Iraq – it is the only area of highway that ISIL controls because [the rest] is all desert land.”
Asked about the Syrian government’s advance, the US-led coalition expressed concern.
“The demonstrated hostile intent and actions of pro-regime forces near coalition and partner forces in southern Syria … continue to concern us, and the coalition will take appropriate measures to protect our forces,” it said in a statement.
“As long as pro-regime forces are oriented toward coalition and partnered forces, the potential for conflict is escalated,” it added.
On Thursday, a US jet shot down a pro-government combat drone that fired what turned out to be a dud bomb close to the coalition’s Al-Tanf garrison near the Jordanian border.
The drone fired into empty space, but the coalition considered it to be a threat.
The Pentagon credited Syria’s ally Russia with helping to calm tensions after the drone incident.
The Pentagon has not said who was operating the drone, but the area near Al-Tanf has seen a surge in activity by Iran-backed troops loyal to Syrian President Bashar al-Assad.
It was the third time the coalition has struck pro-government forces near Al-Tanf in less than a month, as tensions on the border area grow.
“Russia has been very helpful [in resolving these latest tensions] and I think that the calm we see today is largely due to their efforts,” spokesman Navy Captain Jeff Davis said on Friday.
The coalition has established a “de-confliction” zone extending 55km from the garrison, in which pro-government and Russian forces are not supposed to operate.
Syria’s government has been eager to reach the eastern border after recapturing territory in central Homs province once held by ISIL, which stands for Islamic State of Iraq and the Levant, and is also known as ISIS.
The government is hoping to lead the battle against the armed group in the eastern province of Deir Az Zor and head off any attempts by the US-led coalition to do so.
Syria’s government has not held positions on the border with Iraq since 2015, when ISIL swept down from neighbouring Deir Az Zor and captured positions in Homs province, including the ancient city of Palmyra.