Seven Kalibr cruise missiles were launched Thursday from Russia's Velikiy Novgorod and Kolpino submarines in the eastern Mediterranean, the Russian Defense Ministry said.
The Syrian army and its allies recently broke an Islamic State siege of an enclave in Deir al-Zor that had lasted three years.
"The targets were command posts, communication centres, as well as militants' weapons and ammunition stockpiles in areas of south-east Deir Ezzor under the control of Islamic State", the ministry said.
The Britain-based monitor said seven children were among the dead in the strikes, which hit multiple parts of the province including the city of Mayadeen, a remaining IS stronghold. However, they still control rural areas outside the city and the border with Iraq.
Syrian activists say at least 20 civilians have been killed in air and missile strikes across east Syria, where USA and Russian-backed forces are racing to take territory from the Islamic State group's shrinking Euphrates river valley domain.
The militants control less than half the city and are encircled on three sides with their backs to the Euphrates River.
Aziz added that they are about 6 kilometers (4 miles) away from the city's eastern entrance.
While the evacuation, which was negotiated by Lebanon's Hezbollah group, removed the militants from the Syria-Lebanon border, it left both Iraq and the US fuming. The Hezbollah-negotiated deal allowed the evacuation in exchange for locating the remains of Lebanese soldiers and the release of fighters.
The convoy had been stuck in the desert following airstrikes by the U.S-led coalition to prevent its advance. Last week, the U.S-led coalition said it ended surveillance of the convoy after a Russian request.
On Thursday, a surviving Hezbollah fighter was returned to Lebanon.
Both the countries claimed that they should have been killed on the battlefield not moved to the Iraq border.