The government-controlled Syrian Central Military Media said troops are marching south from Deir el-Zour toward Mayadeen under the cover of airstrikes.
As a result of an air strike, more than 60 foreign mercenaries from the former Soviet Union, Tunisia, and Egypt were killed in south of Deir ez-Zor.
Elsewhere near the Jordanian border, the Russian military said the United States is using the refugees living in the Rukban desert camp as human shields to protect its military base in the southeastern town of al-Tanf.
The ministry noted that the armed forces destroyed a command post of terrorists near Meyadin city of Syria and killed up to 80 militants, including nine militants coming from the North Caucasus.
Syrian government forces pushed into one of the last remaining urban strongholds of the Islamic State group in the country's east on Friday, following days of fierce fighting and intense Russian airstrikes that involved cruise missiles from the Mediterranean, activists and officials said.
Some 120 Daesh (the so-called IS) fighters and 60 foreign mercenaries were killed in a series of Russian air strikes in Syria over the past 24 hours, the defense ministry in Moscow said on Saturday.
In central Syria, the attack on the village of Abu Dali in Hama province was led by al-Qaida-linked Hay'at Tahrir al Sham - Arabic for Levant Liberation Committee and also known as HTS.
"With support from Russian aviation, regime forces entered Mayadeen and took control of several buildings in the west of the town", Rami Abdel Rahman, head of the Britain- based Syrian Observatory for Human Rights, told AFP.
Sheikh Muhammad Amlah, a leader of tribesmen fighters alongside the Syrian army, was cited by the pro-government al-Watan daily on Friday as saying that the army is advancing toward Mayadeen city as well as the area of Muhasan and other areas on the eastern bank of Euphrates River.
The advances against IS in Deir Ezzor have cost a heavy civilian death toll from Russian and coalition air raids.
Russian Defense Minister Sergei Shoigu said in August that the recapture of Deir Ezzor would "say a lot, if not everything, about the end of the battle with [ISIS]" in an interview with Russian state broadcaster Rossiya 24.