According to the Syrian military officials, Imam Ali Brigades and Righteous Brigades members were killed in the military action, which took place south of Al-Bukamal, about 150 kilometers east of Deir Ezzor.
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.
Several people were killed and wounded, state media said, without giving precise figures.
The Syrian government has repeatedly denounced the attacks of the Western Coalition forces, led by the United States, against the civilian population and positions of the army, which killed hundreds of residents and soldiers.
Syrian state TV is reporting that the USA -led coalition has struck a military position in the country's east, leaving several troops dead and wounded, allegations denied by a US official.
"Thirty-eight non-Syrian fighters from regime loyalist militias were killed in the night-time raid on Al-Hari, on the Syrian-Iraqi border", said Observatory head Rami Abdel Rahman.
The US-led coalition is supporting an alliance of Syrian Arab and Kurdish militia fighting Islamic State northeast of Albu Kamal.
US military spokesman Col. Sean Ryan said the coalition was looking into the reports.
Kim Summit Gives Families Hope for Closure
At their meeting in Singapore , the two signed a document to bring peace to the Korean peninsula and rid it of nuclear arms. The one-day summit, aimed at reducing the threat from nuclear-armed North Korea, went ahead as planned on Tuesday.
"There have been no strikes by U.S. or Coalition forces in that area", the coalition's press office said.
There are unconfirmed reports there were also Hezbollah and Iranian forces at the military base.
Syrian and Iraqi forces have driven ISIS from virtually all the territory it once held in both countries, but the terrorists still control some remote areas along the border.
IS overran large swathes of Syria and neighboring Iraq in 2014, declaring a "caliphate" in areas they controlled.
The death toll in an overnight bombing raid on pro-regime forces in eastern Syria has risen to 52 loyalist fighters, the Britain-based Syrian Observatory for Human Rights said Monday.
Asked about the reported air strikes, an Israeli military spokeswoman said: "We do not comment on foreign reports".
Israel, alarmed about the clout of arch enemies Iran and Hezbollah, has pressed Russia, Assad's other key ally, to make sure Tehran does not entrench its military sway in Syria.
An Iraqi paramilitary force on Monday accused the United States of America of killing 22 of its fighters in an overnight air raid just inside Syria's border with Iraq that a monitor said left dozens dead.