Seven militant field commanders and more than 1,000 fighters in Syria agreed to side with the government troops, the Russian Defense Ministry said on Thursday in a statement.
American-backed Syrian Democratic Forces are also fighting near the city, advancing from the north bank of the Euphrates river, while Assad's forces move in from the south.
Advanced stealth technology is coupled with 18 torpedoes and eight cruise missiles, which Russian Federation claims will allow the craft to strike land, sea and air targets.
The strikes come as Syria's army battles to oust IS from the provincial capital Deir Ezzor city, after breaking the jihadist group's two-year siege of government-held parts of the metropolis.
They said that while the militants still control rural areas outside the city and the border with Iraq, they are now encircled by Syrian troops from three sides, with their backs to the Euphrates River.
According to Britain-based Syrian Observatory for Human Rights head, Rami Abdurrahman, buses and vehicles carrying about 400 militants and civilians crossed into Deir el-Zour province on Wednesday, but no details were available about where the buses went. The monitoring group said the US -led worldwide coalition, which is supporting non-government forces, was partly to blame.
The advances against Islamic State, another blow to its control over territory it held for years as part of a self-declared caliphate, has raised concerns that it would bring the SDF into closer proximity to the Syrian government side, which is backed by Russian Federation and Iran.