Russia is likely removing nuclear warheads from aging nuclear cruise missiles and firing unarmed munitions at Ukraine, Britain's military intelligence said on Saturday.

The defense ministry said open source imagery shows wreckage of an air launched cruise missile fired at Ukraine which seem to have been designed in the 1980s as a nuclear delivery system, adding that ballast was probably being substituted for the warheads.

Such a system will still produce damage through the missile's kinetic energy and unspent fuel. However, it is unlikely to achieve reliable effects against intended targets, the ministry added in its daily intelligence update posted on Twitter.

"Whatever Russia's intent, this improvisation highlights the level of depletion in Russia's stock of long range missiles," the ministry said.