The attack took place in al-Harra, southeast of the town of Albu Kamal, state media said, citing a military source who gave no breakdown of casualties other than saying there "were several martyrs and others were wounded".
United States forces are also based in Tanf, southwest of Albu Kamal in the Syrian desert near the borders of Iraq and Jordan. At least 52 fighters were killed in the attacks, including a number of Syrian troops.
Syrian troops and allied militias, backed by Russian airstrikes, have been conducting operations west of the Euphrates River, while the USA -backed Syrian Democratic Forces, a Kurdish-led militia, is operating on the eastern banks.
Damascus, Jun 18 (Prensa Latina) A drone attack by the USA -led worldwide coalition killed today 40 Syrian soldiers and allies and injured 30 in a desert area south of al-Bukamal, northeastern of Deir Ezzor province.
"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.
President Bashar al-Assad's army, with the help of Iran-backed militias including Hezbollah and Iraqi groups, drove ISIS from Albu Kamal and its environs past year, but the jihadis have since staged attacks there.
The U.S.is leading a coalition backing Syrian Arab and Kurdish militias fighting against the Islamic State northeast of Albu Kamal.
U.S. Central Command spokesman Maj.
The Syrian Observatory for Human Rights 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.
The only remaining major pockets of militants are found in the US-protected zones of 'interest.' In addition to the coalition's air support, over 2,000 U.S. soldiers are embedded with the SDF in the northeast, as well around Al-Tanf base, established not far from the Israeli-occupied Golan Heights. "We're looking into who that could possibly be, but it wasn't the U.S. or the coalition". They said the base that was hit was 700 meters into Syrian territory and the Syrian government was aware of their presence.
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. "We will act against these efforts anywhere in Syria", Israeli Prime Minister Benjamin Netanyahu said Sunday at a cabinet meeting.
Damascus says it considers the United States an occupying force in Syria and supports any resistance against USA forces.