The Syrian government, which has lost ground to insurgents in the Syrian civil war recently, renewed its assault on the Islamic State group in Aleppo province Thursday using newly arrived Russian jets, according to an independent monitoring group. Russia recently supplied the beleaguered Syrian regime with military equipment such as helicopter gunships, fighter jets, artillery and ground forces.

The fresh airstrikes, which began earlier this week, preceded ground assaults near the Kweiris air base east of Aleppo, where Syrian President Bashar Assad's troops had previously been outnumbered and outgunned by ISIS, according to Britain's Syrian Observatory for Human Rights.

“It’s unknown whether the pilots of the warplanes which arrived from Russia are Russian or Syrian pilots,” noted a report from the Syrian observatory.

Moscow’s increased involvement in the Syrian civil war has worried the U.S. and other Western nations, who believe Russia’s involvement could further destabilize the conflict and possibly lead to a clash between the U.S. and Russian militaries. Russia has been delivering humanitarian and military aid to Syria for over three weeks, while the U.S. has led a bombing coalition against ISIS for more than a year.

Moscow claims that Syria is a Russian ally and that the authoritarian Assad regime should be included in efforts to fight ISIS.

The coalition bombing group, which contains a load of European and Arab states, and the Syrian and Russian governments all consider ISIS an enemy, but are unlikely to work together because of Assad’s murderous reign as leader of Syria. The United States has indicated it would work with Russia against the terror group, but would not support it while Moscow propped up Assad in Damascus.

Russia stepped up support of Syria after ISIS attacked a Russian military base in the North Caucasus region of Russia. Since then the Russian military has established two military bases on Syria's Mediterranean coast.

The civil war in Syria has killed more than 250,000 people and displaced as many as 4 million.