Syrian troops loyal to President Bashar Assad launched a ground offensive against rebels in the country Wednesday, backed by a major display of Russian military power, as airstrikes and cruise missiles pounded opposition and Islamic State group positions. News reports and video of fighting uploaded to the Internet showed that the Syrian army was moving from the city of Hama toward Idlib, a stronghold held by a coalition of mostly Islamic rebels, the Washington Post reported.

The Syrian Observatory for Human Rights reported "the most intense fighting in months" in Hama and Idlib. The clashes followed a wave of Russian airstrikes in the same areas, it said.

During Wednesday’s fighting, rebels fired advanced antitank missiles, supplied covertly by the CIA, at Syria’s Russian-made tanks, leaving the impression of a proxy war between Russia and the U.S., the New York Times reported.

The ground offensive was launched in coordination with a barrage of Russian cruise missiles, fired from ships in the Caspian Sea, almost 1,000 miles away from their targets in Syria. Russia's Defense Minister Sergei Shoigu said four warships fired 26 sea-based cruise missiles at 11 targets. He added that the missile strikes destroyed their targets and caused no civilian casualties, though this claim could not be independently verified. In addition to the cruise missile strikes, Russia also carried out a series of airstrikes on targets in Syria on Wednesday.

Russia has been the focus of some criticism, since it began its military intervention in Syria on Sept. 30. Though nominally targeting militants of the Islamic State group, observers have said that Russia strikes have been responsible for civilian deaths, and had targeted moderate rebel groups backed by the U.S. and its coalition allies.

On Wednesday, U.S. Defense Secretary Ash Carter said that coalition forces fighting the Islamic State group -- also known as ISIS or ISIL -- in Syria would not cooperate with Russia, the BBC reported.

"We believe Russia has the wrong strategy," he said. "They continue to hit targets that are not IS. We believe this is a fundamental mistake."

Tensions between coalition forces, including the U.S., operating in Syria and Russia have spiked in recent days, following repeated incursions by Russian fighter aircraft into NATO member Turkey's airspace.

Russia's defense ministry had said that an SU-30 fighter jet had entered Turkish airspace along the border with Syria "for a few seconds" Saturday, and characterized the incident as a mistake caused by bad weather, according to Al-Jazeera. Officials said they were investigating another alleged incursion, which NATO said took place Sunday.