MOSCOW, May 11 (Xinhua) -- The Russian Foreign Ministry said Tuesday that it is expelling an assistant defense attache at the Romanian embassy in Moscow in tit-for-tat retaliation.

The Romanian ambassador was summoned to the Russian Foreign Ministry, where he received a note demanding this officer leave Russia within 72 hours.

The ministry said the move was a response to the unjustified expulsion of an assistant military attache at the Russian embassy in Bucharest on April 26.

The mutual expulsions came amid a fresh diplomatic row over the past weeks between Russia and Western countries, including so far the United States, Italy, the Czech Republic, the three Baltic states, Slovakia, Poland, Ukraine and Romania.

Russian President Vladimir Putin has ordered the government to blacklist "unfriendly countries" and vowed necessary sanctions.