Russian special forces are helping Syrian government troops fight Islamic State militants in the battle for the strategic city of Deir el-Zour in eastern Syria, the defense ministry in Moscow said Thursday.

Russia began its operation to support President Bashar Assad’s offensive against the IS in Syria in 2015 but has mostly focused on providing air cover to government troops on the ground.

The campaign for Deir el-Zour, Syria’s largest eastern city, is caught up in a race between government troops and the U.S.-backed Syrian Democratic Forces.

Russian-backed troops advance

In the past two weeks, the pro-government forces, backed by Russian air cover and Iranian-allied militiamen, gained control of most of the city and crossed the Euphrates River to the area of SDF operations.

Maj. Gen. Igor Konashenkov, the Russian defense ministry’s spokesman, said in a statement that Russian special forces have been deployed to help Syrian government forces fighting the IS militants outside Deir el-Zour.

A Syrian government offensive late Wednesday captured two villages on the Euphrates’ western bank, liberating about 16 square kilometers (6 square miles) of land, Konashenkov said.

Konashenkov also said the Syrian Democratic Forces shelled government positions outside Deir el-Zour twice in recent days and warned the U.S.-led coalition that Moscow would have to retaliate if the Russian troops in the area were to come under fire.

Raqqa battle nearly won

The development comes as the battle for the IS stronghold of Raqqa, north of Deir el-Zour, is reaching its final stages, the SDF said Wednesday, four months after the offensive began.

The Kurdish-led SDF said it captured Raqqa’s last grain silos from the militants in a surprise offensive on the city’s northern neighborhoods. Less than 300 militants remain holed up in the city, which has witnessed an intense bombing campaign, particularly in the last few days, according to the Britain-based Syrian Observatory for Human Rights that monitors the war.

The campaign to take Raqqa began in June in a quick advance after a breach of the wall of the Old City, a major fortification for the militants. But it has since slowed down as the forces faced mounting resistance from the militants.

The Russian defense ministry, however, claimed Thursday that its intelligence shows the coalition’s operation in Raqqa had stopped, and that SDF fighters have been redeployed from there to Deir el-Zour.