The historic city of Palmyra was re-captured by Syrian government forces in late March
The Islamic State (IS) group on Tuesday cut a key supply route between Syria's Homs and the world heritage site of Palmyra just weeks after the army recaptured the ancient city, a monitor said.
IS "was able to cut the supply road between Homs and Palmyra near the Tayfur military airport after an attack launched from the east of Homs," the Syrian Observatory for Human Rights said.
Both cities are controlled by the government after troops recaptured Palmyra - a UNESCO world heritage site - from the militant group in late March, backed by Russian air strikes.
Cutting the road "came as part of IS's biggest assault since the army recaptured Palmyra with Russian support" on 27 March, Observatory chief Rami Abdel Rahman said.
"Violent clashes between regime forces and Daesh are ongoing," he said, using an Arabic acronym for the group.
"Daesh surrounds Palmyra from all angles except in the southwest," Abdel Rahman said, adding the closest IS was to the city was 10 kilometres.
IS and the government both control parts of the area between Homs and Palmyra.
The road IS cut is "the main road between Homs and Palmyra but not the only one as there are other side roads" between both cities, Abdel Rahman said.
On Wednesday, IHS Jane's revealed that Russian ground forces had set up a forward operating base in Palmyra and installed an air-defence system to help protect the site.
The Russian base is located just to the west of the city, with Fakhr-al-Din al-Maani Castle less than 1.5 km further to the west, and the ruins to the south.
Syria's civil war has killed more than 270,000 people and displaced at least 12 million people since it started with anti-government protests in 2011.
The Britain-based monitor gathers its information from a wide network of sources inside Syria.