Russia has postponed indefinitely all flights of Su-24 Fencer tactical bombers after one of them crashed in Russia’s Urals, a source in the Defense Ministry said on Tuesday.

The Su-24 combat aircraft crashed in the woods of the Kurgan region during a routine flight on Monday. Both pilots ejected safely.

“The Air Force commander has cancelled all flights of this type of aircraft until the cause of the crash is established,” the source said but did not specify how long it could take.

Monday’s crash was the third of a Su-24 in Russia over the last four months with the two previous crashes occurring in October and December 2011.

The Su-24 is a two-seat, twin-engine fighter-bomber similar to NATO's Tornado and Mirage 2000 planes.

The plane has been in service with the Russian Air Force since the mid-1970s. However, in recent years Russia has gradually been phasing out the planes, which have a patchy safety record.

According to the Defense Ministry’s plans, the Su-24 will be gradually replaced with new Su-34 Fullback strike aircraft, which has the potential to become the top plane in its class for years to come.