At a Kremlin ceremony which saw Putin bestow state awards on the widows of the scientists killed in the accident, Putin also said their husbands did not die in vain.

"The very fact of possessing such unique technologies is the most important and reliable guarantee of peace on the planet," Putin said in comments broadcast on state television on Friday.

"And despite everything we will certainly perfect this weapon."

Seven people including five employees of Russia's state nuclear agency Rosatom were killed in an explosion at a missile test site in the far northern Arkhangelsk region in August.

A brief rise in local radiation levels sparked panic in northern Russia as well as fresh Western concerns over Russia's military nuclear power capabilities.

Western experts have linked the blast at the Nyonoksa test site to the 9M730 Burevestnik nuclear-powered cruise missile first revealed by Putin in 2018 and which has the NATO codename 'Skyfall'.

The Russian authorities have, however, not confirmed that the accident was linked to the Burevestnik project and the identity of the missile that exploded remains uncertain.

Putin stressed that the weapon the Russian scientists had worked on had no foreign equivalent.

"We are talking about the most advanced technical ideas and solutions, about weapon which is without equal in the world," Putin said at the ceremony late Thursday.

"About the weapon which is designed to secure Russia's sovereignty and security for decades to come."

Handing the Order of Courage to the black-clad widows, Putin said Russia would always be proud of their husbands and support their families.

"They were in charge of very complicated, serious and critically important work," he added, calling them top-notch professionals.

"They had a special mission," he said.

"One day we will all pass. The question is, how did we live? Your loved ones lived an honourable life."