Russian anti-aircraft defences would be incapable of reaching North Korean ballistic missiles, a former Russian air force commander told the Interfax news agency on Tuesday.
"If North Korean missiles enter Russian air space, the S-300 anti-aircraft defence systems in the Russian Far East could not destroy them," General Anatolyi Kornukov said.
"This system is not designed to destroy ballistic missiles." The most modern anti-aircraft defences - the S-400 Triumf - would be up to the task, but these systems have not been tested outside Moscow, the general added.
North Korea carried out its latest nuclear test on May 25, and defied global condemnation by firing five short-range missiles.
Kim Jong-Il's regime has since renounced the truce that ended the Korean war in 1953, straining already tense relations with the South.
The hardline communist state is reported to be preparing to test-fire a long-range missile capable in theory of reaching Alaska from a northwest base, as well as several medium-range missiles from along its southeast coast. Kim reportedly named his youngest son as the eventual heir to his family dynasty on Tuesday.