Grigory Klinishov, who was in his 90s, has reportedly died by suicide in Moscow.

Klinishov, who was in his early 90s, was reported to have died on June 17. A suicide note was found next to his body at an apartment residence in central Moscow, Russia’s TASS news agency reported on Wednesday.

According to Russian-language state media, an investigation has been opened into the death of Klinishov, who was born in 1930 and was among the creators of Russia’s RDS-37 – a thermonuclear bomb that was first tested in 1955, according to the RIA Novosti news agency.

The yield from RDS-37 was so powerful when dropped from a Russian bomber at a test site that shockwaves broke the windows within a radius of 240km (149 miles) from the epicentre of the blast, according to the Russian-language Mediazona news outlet. Casualties were also reported due to the test explosion causing structures to collapse, including a young child who died in a small town approximately 75km (47 miles) away .

Klinishov also helped develop several types of newer-generation thermonuclear bombs, which are also known as hydrogen bombs or H-bombs, according to Russian language media reports.

Russian nuclear physicist Grigory Klinishov, who helped create RDS-37, the USSR’s first two-stage hydrogen bomb, reportedly killed himself today. At the age of 92, he’d apparently seen enough (or didn’t want to see what comes next). https://t.co/sg4DvDjdtv

— Kevin Rothrock (@KevinRothrock) June 21, 2023

News of Klinishov’s death comes as Russia’s President Vladimir Putin reiterated plans on Wednesday to strengthen his country’s nuclear forces, the Interfax news agency reported.

Putin said that Russia’s new generation of Sarmat intercontinental ballistic missiles – code-named Satan by NATO allies – which are capable of carrying 10 or more nuclear warheads, would soon be deployed for combat duty.

Putin also stressed the importance of Russia’s “triad” of nuclear forces that can be launched from land, sea or air, according to Interfax.

“The most important task here is the development of the nuclear triad, which is a key guarantee of Russia’s military security and global stability,” Putin said in a speech to new graduates of military academies.

The first Sarmat launchers would be put on combat duty “in the near future”, he added.