North Korea's threat of "indiscriminate" strikes came just hours before South Korea and the US began annual, large-scale military drills, which usually provoke a hardline response from Pyongyang.
"We consider the public statements (by North Korea) threatening its adversaries with 'pre-emptive nuclear strikes' to be completely unacceptable," the ministry said in a statement.
"Pyongyang must realise that in doing so, North Korea is definitively turning its back on the international community and creating a legal basis for the use of military force against it," the ministry said.
The situation is particularly volatile this year, given the North's recent nuclear test and long-range rocket launch and its fury over new UN sanctions imposed in response.
Russia -- which enjoys friendly ties with the reclusive Stalinist regime -- had on Friday already voiced "deep concern" after North Korean leader Kim Jong-Un ordered that his country's nuclear arsenal be readied for pre-emptive use at any time.
