Russia on Thursday accused the US-led coalition of deploying missiles against Syrian troops at a garrison in the east of the country, where rebels battling the Islamic State group are being trained.
In a statement, the defence ministry said the "United States has moved two HIMARS multiple rocket launchers from Jordan to the Al-Tanaf US special forces base."
That suggested that the equipment would be used for strikes against Syrian government forces, the statement added.
"Deploying any type of foreign weapons on Syrian territory... must be approved by the government of the sovereign country," it said.
"Forces of the US-led anti-IS coalition have repeatedly issued strikes on Syrian government forces fighting IS near the Jordanian border.
"It's not hard to guess that similar strikes will be continued against contingents of the Syrian army in the future using HIMARS," it said.
In Washington, a US Defense Department confirmed the deployment of the HIMARS system to the base, but did not say how many.
Russia has conducted a bombing campaign in Syria in support of President Bashar al-Assad since September 2015, and last week branded a coalition strike on pro-regime fighters an "act of aggression."
Last week the Pentagon credited Russia with helping to calm tensions in southern Syria after a US jet shot down a pro-regime combat drone that had fired at coalition forces.
In the first incident of its type, the pro-regime drone on fired what turned out to be a dud bomb at US-led coalition forces close to the coalition's At-Tanaf garrison near the Jordanian border.
Pentagon spokesman Navy Captain Jeff Davis said then that any escalation in hostilities between the coalition and the pro-regime forces had been avoided thanks mainly to Russia's influence.
The HIMARS system, mounted on a lorry, fires GPS-guided rockets with a range of 70 kilometres (43 miles).
Another version of the system fires small GPS-guided missiles with a range of 300 kilometres, but it is not know which type has been deployed
