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Russia is believed to be sending its generals to the front line of its war in Ukraine in a bid to bolster low morale among troops.
The Russian President is said to be frustrated at the lack of progress, which has seen his troops fail to seize any major cities despite heavy bombardment of them.
On Thursday Ukrainian officials claimed a fourth Russian general has been killed during fighting in the city of Mariupol.
Watch: Who are the dead Russian military officers and what do their deaths mean?
"We think that one of the reasons why a number generals appear to be killed is because things are going badly they have to go closer to the front to guide their troops… to provide more supervision," one Western official said.
"Therefore, they’re going further forward and therefore becoming vulnerable to enemy action."
Answering a question about the role of the Russian Air Force and its vulnerability to Ukrainian countermeasures, he added: "I think we are seeing a reasonable amounts of evidence of very, very low morale amongst the Russian forces which may well be playing into the ... necessity of senior officers to go to the front."
On Thursday, Ukraine said Major General Oleg Mityaev became the fourth Russian general to be killed in the war in Ukraine.
Fellow officers Major Generals Andrei Sukhovetsky, Vitaly Gerasimov and Andrei Kolesnikov have all also been reported dead by Ukrainian officials in separate incidents.
Only the first — Major General Andrei Sukhovetsky — has been confirmed by Russia.
According to some reports, analysts believe that around 20 generals are leading Russian operations in Ukraine.
One source close to Ukrainian President Volodymyr Zelenskyy has claimed that a special unit has been set up to hunt senior Russian commanders, but other suggestions are that their presence near the fiercest fighting is to boost faltering morale among troops.
As of Thursday morning, Ukraine's State Service of Special Communications and Information Protection (SSSCIP) claimed a total of 14,000 Russian troops had died in the conflict.
Russian is continuing its offensive in Ukraine. On Wednesday a theatre in the besieged city of Mariupol, where hundreds of people were sheltering, was hit, while 80% of residential housing in the city is said to have been destroyed.
Despite the continuing offensive, British defence intelligence analysts believe Russia is being forced to divert “large numbers” of troops to defend its supply lines.
In its latest intelligence briefing, the Ministry of Defence said: "The Russian invasion of Ukraine has largely stalled on all fronts.
"Russian forces have made minimal progress on land, sea or air in recent days and they continue to suffer heavy losses.
"Ukrainian resistance remains staunch and well-coordinated. The vast majority of Ukrainian territory, including all major cities, remains in Ukrainian hands."