Russia announced new military exercises involving bombers and fighter jets on Monday in a show of strength near the border with Ukraine.
An air force spokesman was quoted by Interfax news agency as saying more than 100 planes and helicopters would take part in the manoeuvres from Monday until Friday in its central and western districts.
The spokesman, Igor Klimov, said the exercises were the first in a series to improve coordination in the military and made no mention of Ukraine, where pro-Russian rebels are fighting Ukrainian government forces.
The move is likely to alarm Western powers which have accused Russia of beefing up the number of troops along its border with Ukraine and arming the rebels in eastern Ukraine. Moscow denies supplying the rebels with weapons.
Klimov said aircraft such as Su-27 and MiG-31 fighter jets, Russia's newest frontline bomber Su-34, and Mi-8, Mi-24 and Mi-28N helicopters would be used in the exercises and the aircraft would conduct missile practice.
The aircraft will be testing "aircraft weapons on land and air targets on new ranges, and will be conducting real and electronic launches of anti-aircraft missiles in Ashuluk (Astrakhan region in southern Russia) which is specifically designed to aide the coordination between aviation and anti-missile defence", he was quoted as saying.
Russia's Defence Ministry could not immediately be reached for comment.
Fighting in eastern Ukraine has intensified, with Kiev stepping up a campaign to squeeze rebels in their two main strongholds of Donetsk and Luhansk after the West accused the rebels of shooting down a Malaysian airliner last month.
An official from Russia's FSB security service in the Rostov region, just across the border from Ukraine, was quoted as saying more than 400 Ukrainian troops had asked for asylum in Russia.
"During the night 438 Ukrainian soldiers asked Russian border guards about asylum," Itar-Tass news agency quoted Vasily Malayev as saying.
The West criticised Russia for staging earlier military exercises near Ukraine. In March, Russia sent 8,500 artillery personnel to the border, armed with Grad (Hail), Hurricane and Tornado multiple-rocket launchers, for exercises.
In May, Russia said it had pulled back forces near the border, but NATO accused Moscow of boosting the number of troops and weaponry along the border late last month.