A retired highly-decorated US Air Force general says the Russian air campaign in Syria is “very definitely effective” because it has been targeting militant groups fighting the Syrian armed forces.

“Russia means business,” retired Air Force Lt. Gen. Thomas McInerney told The Washington Times.

McInerney said Russia is flying more missions over Syria than the US, intimidating the militants. However, he accused Moscow of running an indiscriminate campaign that has “lots of collateral damage.”

The former general’s comments came as a Washington-based research group has concluded that the Russian airstrikes are primarily hitting US-backed militants fighting the government of President Bashar al-Assad.

The Institute for the Study of War says Russian warplanes and helicopter gunships fly only a smattering of sorties against the Daesh (ISIL) positions.

The study, “Russian Air Strikes in Syria,” states that Russia is coordinating its target list with Syrian ground forces in militant strongholds in the northwestern regions.

The assessment corroborates the Pentagon’s assertions that the primary objective of Russian President Vladimir Putin since he launched the air campaign on September 30 has been to destroy the US-backed militants-- a linchpin of President Barack Obama’s strategy in Syria.

President Putin (R) shakes hands with his Syrian counterpart during a meeting at the Kremlin in Moscow on October 21, 2015. (AFP photo)

The United States -- with assistance from its regional allies especially Turkey, Jordan and Saudi Arabia -- has been arming and training militant units to combat the Syrian government.

US Secretary of State John Kerry and Saudi Arabia’s King Salman pledged Friday to further boost the militants operating in Syria, while stressing the need for a “transition away” from President Assad.