The country's Investigative Committee, which is responsible for probing major crimes, said it had opened an investigation into flight preparation rules.

"On December 9, 2025, during a test flight, an AN-22 aircraft crashed near the village of Ivankovo in the Ivanovo region," the committee said.

"All crew members onboard were killed."

It did not say how many people were on the plane, but the TASS state news agency earlier reported the plane had seven crew members.

The defence ministry earlier said the flight took place after repair work.

"Today in the Ivanovo region, during a test flight following repairs, an AN-22 military transport aircraft crashed," state media quoted the defence ministry as saying in a statement.

"The plane went down in an uninhabited area," it added.

Search crews had been deployed, the defence ministry said.

The Ivanovo region is located around 200 kilometres (125 miles) east of Moscow.

There was no suggestion that the incident was connected to Russia's offensive on Ukraine or accusations of involvement by Kyiv.

Accidents involving military transport and equipment have become more frequent in Russia during its almost four-year campaign in Ukraine, which has seen increased military movement and activity in the country.