So far, Russia has only confirmed the death of one general but Kyiv and Western officials believe up to seven have been killed since the invasion started on February 24. 

Rezantsev's death comes after he gloated to a Russian soldier that the war would be over within hours, just four days after it began, in a conversation intercepted by the Ukrainian military, BBC reported. 

The airbase where Rezantsev was reportedly killed is being used as a command post for Russia but it has been attacked by the Ukraine army several times, with another lieutenant general, Andrei Mordvichev, reportedly killed by a Ukrainian strike on March 18 at the same base.

Lieutenant generals are normally positioned back from the frontline but morale has been low among Russian forces, forcing generals to get more directly involved in the battles, according to the BBC. 

The low morale among Russian forces reportedly saw Col Yuri Medvedev deliberately run over by his own men with a tank this week. The 37th Motor Rifle Brigade reportedly turned on him after casualties in their unit.

Medvedev reportedly had his legs injured due to the incident and was taken to hospital where he died, a western official said. 

The BBC reported Russian forces were relying in part on open communication systems, for example, mobile phones and analogue radios, which are easy to intercept and could give away the locations of high-ranking officers.

Russia's invasion of Ukraine has been ongoing since February 24 with the UN human rights office saying on Friday at least 1035 people have been killed and 1650 wounded - 90 children among the dead.

It's believed the true figures are considerably higher due to delays in reporting from areas with intense hostilities, including the southern besieged city of Mariupol.