MiG-31I fighter jets have been upgraded and received an air refueling system to increase the combat radius, a defense industry source told TASS.

"MiG-I fighters of the Russian long-range aviation received a possibility to refuel in the air and increased the combat engagement distance," the source said.

Another source said MiG-31I differs from previous MiG-K option by "different engines, avionics and missiles."

TASS has no official confirmation of the report.

The Izvestia daily earlier said MiG-31I will be able to refuel in the air. The fighter has electronic systems that increase the flight characteristics and capabilities. The jet is equipped with an electronic remote control system and onboard computers that automatically bring the jet into the required trajectory and fire a hypersonic missile at the calculated time.