India will ground all its Soviet-era Russian fighter jets, the MiG-21, by 2025, following the death of two officers in a crash, the latest in a series of casualties involving the single-engine jet’s failure, a newspaper reported on Saturday.

The Times of India quoted unnamed Indian Air Force officials as saying the MiG-21s have long past their retirement but must be replaced before being grounded.

The report did not specify what portion of India’s fighter-jet capability would be affected. The Wion news outlet said the air force has around 70 MiG-21s. The air force and defence ministry have been buying aircraft from Western makers in recent years.

A senior defence ministry official declined to confirm or deny the Times of India report, telling Reuters only that discussions on the future of the MiG-21 were underway, as sourcing of spare parts from Russia was increasingly difficult due to the war in Ukraine.

A defence ministry spokesman did not immediately respond to a message seeking comment.

The MiG-21, dubbed “flying coffins” by the Indian press, has been the country’s key fighter jet since its introduction in 1963 but has been plagued by crashes in later years.

The jets have been a critical security asset in India’s military infrastructure, used for example to strike neighbour Pakistan after an alleged suicide attack in the occupied Kashmir region in 2019.

Thursday’s crash of an air force MiG-21 Bison in the desert state of Rajasthan brings to six the number of MiG-21 crashes since last year, with five officers killed, according to official data and a source.

In 2012, then-Defence Minister A.K. Antony told parliament that more than half of India’s 872 MiG-21s had been lost to crashes over the previous four decades.