The GRU stands for Glavnoye Razvedyvatelnoye Upravlenie, (Russian: Chief Intelligence Office), Soviet military intelligence organisation.
Russia has admitted to losing its first GRU military intelligence spy in the war - the latest high-profile casualty of the savage Ukraine invasion.
The GRU stands for Glavnoye Razvedyvatelnoye Upravlenie, (Russian: Chief Intelligence Office), Soviet military intelligence organisation.
Captain Alexey Glushchak, 31, from Tyumen in Siberia, died in the carnage in Ukrainian port Mariupol, but the Russians have given no details of how he was killed.
'Due to the strict secrecy of the military operation, the circumstances of the death of the Tyumen hero are not disclosed,' said a statement.
Pictures emerged of father-of-one Glushchak's funeral in Russia, where he was buried with full military honours and a guard of honour, despite Russia hiding 'thousands' of deaths from those back at home, Daily Mail reports.
Putin's stalling invasion has so far seen the loss of 12 commanders including three generals.
Glushchak was killed fighting near Mariupol, the Russian military said, as it acknowledges losing a GRU officer for the first time.
On the day the military intelligence officer died he had spoken to both his wife and mother in Russia, it was revealed.
He called to congratulate them on International Women's Day but on the same day in the evening they learned he had been killed.
He will be posthumously decorated.
Two elite paratrooper intelligence officers were also revealed to have been killed as the toll worsens for Vladimir Putin’s forces.
Georgy Dudorov, deputy commander of the reconnaissance company for the 137th regiment of the 106th Tula Guards Airborne Division, was acknowledged as dead.
Another paratrooper intelligence officer killed was Aleksey Aleshko, a graduate of the prestigious Ryazan Guards Higher Airborne School.
It follows the loss of Major General Andrei Kolesnikov of the 29th Combined Arms Army last week, the third general to be killed in battle of the 20 taking part in the invasion.
His death came four days after the killing of Major General Vitaly Gerasimov, 45, the first deputy commander of Russia's 41st army.
The general took part in the second Chechen war, the Russian military operation in Syria, and the annexation of Crimea, winning medals from those campaigns.
According to reports, Gerasimov was the son of Valery Gerasimov - the Chief of General Staff of Russia's armed forces.
And Major General Andrei Sukhovetsky, 47, deputy commander of the 41st Combined Arms Army of the Central Military District, was killed.
Sukhovetsky died during a special operation in Ukraine, his comrade-in-arms Sergey Chipilev wrote on social media.
He was shot and killed by a sniper near Mariupol, which has been under a brutal siege by Russian forces for days.
Their deaths coincide with the first expressions of anger and dismay on the toll of coffins now returning to Russia.
Accurate numbers of Russian troops killed in fighting are hard to come by. Ukraine claims 12,000 have been killed, but has not updated that figure for several days.
European and American estimates are lower - between 2,000 and 6,000 - while Russia has only acknowledged around 500 deaths.
The GRU was behind the poisoning with Novichok of its former spy Sergei Skripal - who had defected to Britain - in Salisbury.
Moscow has given no up-to-date total of those killed in the war and named only a handful of the fallen, which include several generals.
Many funerals currently visible in the media are for soldiers slain at the end of February.
Russia is taking two weeks or more to transport their bodies back to relatives, many of whom live in the Russian Far East thousands of miles from the bloody war zone.
The pain is evident in an increasing number of hostile and anguished posts.
'When will this stop, we are seeing coffins almost daily?' said one.
'Why did we need to send our boys into this hell?' asked another.
A funeral was also held for Corporal Danil Novolodsky, 24, a senior gunner on an air assault artillery battery.