Russia's United Aircraft Corporation (UAC) has delivered a new batch of Su-57 and Su-35S fighter jets to the Russian Air Force, the corporation's officials said in a statement.

According to the press release, fifth-generation Su-57 fighters successfully passed all factory tests and were approved by the technical staff of the Ministry of Defense after a series of flight tests in various operational modes.

The planes have been moved to their base, and Russian military pilots have expressed satisfaction with their performance.

"The plane shows high flying and technical characteristics, which were highly appreciated by our pilots," said Vladimir Artyakov, First Deputy General Director of Rostec.

He also confirmed that additional Su-57 aircraft are in various stages of production, and Su-35S aircraft are also nearing completion.

The UAC production facility is currently undergoing modernization to accommodate the increased demand for the Su-57.

Recent upgrades include the completion of new flight test facilities, and construction has begun on additional buildings to support serial production of the fifth-generation aircraft.

"The number of fifth-generation fighters delivered to the Russian Air Force is increasing every year. The Su-57 remains the most advanced front-line aircraft in Russia today," said UAC CEO Yuriy Slyusar.

However, some prominent military figures, including Ilya Tumanov, who runs the influential Russian defense channel Fighterbomber, have expressed concern about the delivered aircraft.

"I hope these are new aircraft, not ones that have been repaired, modernized or refurbished," Tumanov noted, alluding to the recent damage to several Su-57s at their base in Akhtubinsk.

In a Ukrainian drone strike earlier this year, one Su-57 was destroyed and four others were seriously damaged.