A military source said Syrian army's Tiger Forces killed Abu Obeidah al-Najdi, a Saudi who led IS forces in the Deir Ezzor countryside
Syrian troops seized a suburb of the city of Deir Ezzor in eastern Syria on Sunday, tightening the noose around Islamic State (IS) group militants, a military source said.
The Syrian army claimed to have killed one of the highest ranking leaders of IS during its advance in the northwestern countryside of Deir Ezzor on Sunday.
A military source said the army's Tiger Forces killed Abu Obeidah al-Najdi, a Saudi who led IS forces in the northwestern countryside of the province, al-Masdar News reported.
Oil-rich Deir Ezzor province, which borders Iraq, is IS's last major foothold in Syria.
The Syrian army pushed into Deir Ezzor city this month, with Russian air power and Iran-backed militias, breaking an IS siege of an enclave that had lasted three years.
Russia's RIA news agency cited an unnamed source as saying that the Syrian army cut IS's main supply line in the city on Sunday after taking control of the al-Jafra district.
The Syrian military source said the army and allied forces captured al-Jafra on the western bank of the Euphrates. IS militants could only escape across the river.
"They have no outlet except crossing the Euphrates towards the eastern bank and fleeing towards the desert, or [the towns of] al-Bukamal and al-Mayadin," the source told Reuters.
The British-based Syrian Observatory for Human Rights said the army and its allies took al-Jafra and other villages near the city's air base overnight.
IS militants still hold nearly a third of the city, the war monitoring group said. Russian jets pounded movements across the river as IS militants tried to escape in ferries, it added.
Many civilians, including families of the militants, had also tried to flee through the river in recent days, the monitor said.
Separate air strikes by Russia and by the US-led coalition had killed more than 30 people across Deir Ezzor province over the past day, it said.
IS has fallen back on towns downstream of Deir Ezzor and controls much of the desert region around the city, near the border with Iraq. Its militants have also come under attack there from a separate US-backed offensive.
An alliance of Kurdish and Arab militias is battling IS in the northern parts of Deir Ezzor province, with jets and special forces from the US-led coalition.
The Syrian Democratic Forces alliance said it had taken 14 villages and farms, two large towns, and some factories on the eastern bank of the Euphrates since launching its assault last week.
The two offensives have advanced from opposite sides of the river, which bisects Deir Ezzor province and has often served as a dividing line between Russian and US battles against the Islamic State group in Syria.