MOSCOW (Reuters) - Russia considers South Korea's decision to impose sanctions against Russian individuals and entities as an "unfriendly" move and will respond in due course, Russian Foreign Ministry spokeswoman Maria Zakharova said on Wednesday.

       South Korea has imposed sanctions against two Russian vessels which it says were carrying military cargo to North Korea. Seoul said on Tuesday it had also sanctioned two Russian organisations and two Russian citizens linked to Pyongyang's nuclear and missile programmes.

       "This is an unfriendly move by Seoul and is deeply regrettable. The imposition of - I emphasise - illegitimate sanctions will have a negative impact on relations with Russia," Zakharova told reporters at her weekly briefing.

       "Russia is developing good neighbourly ties with friendly North Korea in accordance with the norms of international law, without harming the national security of (South Korea)," she added.

       Ties between Moscow and Pyongyang have strengthened following North Korean leader Kim Jong Un's visit to Russia's far east last year.

       Last week Russia vetoed the annual renewal of a panel of experts monitoring enforcement of United Nations sanctions against North Korea over its nuclear weapons and ballistic missile programs.

       The move came amid U.S.-led accusations that North Korea has transferred weapons to Russia for use in its war in Ukraine. Both Moscow and Pyongyang have denied the accusations, but vowed last year to deepen military relations.

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       Zakharova on Wednesday reiterated that Moscow remained committed to U.N. Security Council resolutions on North Korea "in their entirety" but added that sanctions on Pyongyang were not working as intended.

       "It is clearly seen that endless sanctions are completely useless for achieving the designated goals. They lead to a financial and economic blockade of an entire state with all the ensuing consequences for the population," she said.

       Zakharova accused the United States of seeking to foment "instability" on the Korean peninsula.

       "South Korea apparently lacks the immunity to protect itself from Washington's external influence," she added.

       (Reporting by Dmitry Antonov; Editing by Gareth Jones)