A commander in a pro-government alliance meanwhile told Reuters news agency that several Iraqi militiamen had been killed in strikes by drones, "probably American", on positions between Albu Kamal and al-Tanf - an area 230km (145 miles) to the south-west where some United States military personnel are based.
Artillery are seen lined up in the village of Suway'iah, near the Syrian border town of Albu Kamal, on November 10, 2017.
Syrian President Bashar Assad has blasted the USA presence in Syria, referring to it as an occupation.
It said several people were killed and wounded but did not give a specific number.
However, U.S. Central Command said no member of the U.S. -led coalition carried out strikes in the area.
The US-led coalition against the Islamic State group on Monday denied Syrian government accusations that it carried out a deadly overnight air strike on pro-regime forces in the country's east.
Iraq's Popular Mobilisation Forces, a grouping of mostly Iran-backed Shi'ite paramilitaries, said a US air strike on the Iraqi border with Syria killed 22 of its members and wounded 12 others.
The Syrian army, alongside allied Iran-backed militias including Lebanon's Hezbollah and Iraqi groups, drove Islamic State from Albu Kamal and its environs a year ago, but the jihadists have since staged attacks in the area. Last week they launching an attack on Boukemal that reached the outskirts of the town before being driven back by Syrian government forces.
The Syrian Observatory for Human Rights, a war monitor, said unidentified planes had struck Lebanon's Shi'ite Hezbollah and other allied foreign militias around Albu Kamal.
US forces are also based in Tanf, southwest of Albu Kamal in the Syrian desert near the borders of Iraq and Jordan.
Details on the strike were still scant, but USA officials say no airstrikes took place by any coalition members in the area.
President Donald Trump in March said that the U.S.