By Andrew Osborn
(Reuters) -British military intelligence said on Tuesday that a weekend drone attack on an airfield deep inside Russia which Moscow blamed on Ukraine is highly likely to have destroyed a nuclear-capable TU-22M3 supersonic long-range bomber.
Kyiv, which on Monday claimed to have attacked another Russian military airfield, says Russia has used the TU-22M3 to bomb targets across Ukraine with conventional munitions. Western military experts believe Russia has around 60 of the aircraft.
The destruction of the plane, which can be fitted with conventional or nuclear warheads, underscores the vulnerability to drone attack of Russia's fleet of ageing but lethal long-range bombers that are a major part of Moscow's war effort.
According to satellite imagery reviewed by Reuters, the attack prompted Russia to relocate other planes of the same type from the airfield to alternative bases further from Ukraine.
Unconfirmed media reports said they had been flown to a base in northern Russia.
Russia's Defence Ministry said the attack on Saturday on one of its military airfields in the Novgorod region had been carried out by a Ukrainian drone and that one plane had been damaged. It gave no more details.
Satellite images taken two days after the attack - on Aug. 21 - of the same airfield seen by Reuters showed a burnt patch of land, a gap, and judging from the shape, what appears to be the remnants of an aircraft on the tarmac where images of the same site on Aug. 8 had shown a military plane.
There was no immediate comment from Ukraine, which rarely takes public responsibility for such attacks, though it has said it will do everything it can to degrade Russian military assets.
Russia, which has designated Britain a hostile country because of its military and financial support for Ukraine, did not comment on the British damage assessment.
In a regular update on Ukraine, British military intelligence said "a Tu-22M3 BACKFIRE medium bomber of Russia's Long Range Aviation (LRA) was highly likely destroyed at Soltsy-2 Air base in Novgorod Oblast, 650 km (403 miles) away from Ukraine’s border".
"This is at least the third successful attack on LRA airfields, again raising questions about Russia’s ability to protect strategic locations deep inside the country," it said.
Russia's Defence Ministry said on Saturday the attack had been carried out by a Ukrainian copter-style drone which had been shot down by small arms fire and that nobody had been hurt.
British military intelligence said that if a copter-style drone had really been used, it added weight to the idea that attacks were being launched from inside Russia as such drones were unlikely to have had the range to reach the airfield from outside Russia.
Russia has often used TU-22M3 planes to bomb Ukraine, it added, criticising what it called the "notoriously inaccurate" heavy anti-ship missiles which the plane fires.
Russia says it uses high-precision missiles to strike targets and does not deliberately target civilians or civilian targets, an assertion Kyiv and its allies reject.
(Reporting by Andrew OsbornAdditional reporting by Eleanor WhalleyEditing by Gareth Jones and Giles Elgood)