Stockholm (AFP) - A Swedish diplomat has been expelled from Moscow in a tit-for-tat move after the Scandinavian country recently kicked out a Russian diplomat, Stockholm's foreign ministry said Monday.

"Russian authorities have informed us that a diplomat at the Swedish embassy has to leave the country ... Russia has made it clear it considers this to be a response to the Swedish decision to expel a Russian diplomat," foreign ministry spokesman Johan Tegel told AFP.

Neither the names nor the positions of the two diplomats were disclosed.

The Russian diplomat was expelled because of actions "not in line with the Vienna Convention" which governs diplomatic relations, Tegel said, providing no further details on the nature of the Russian's actions nor the exact timing of that expulsion.

"I can only say it was recently," he added.

Tegel said it was too early to tell how Moscow's decision would affect relations between the two countries.

"But it won't improve the state of our relations," he said.

Swedish Defence Minister Peter Hultqvist said in June that Sweden, a non-NATO country, was stepping up its military capabilities and exercises with the alliance amid concerns over Russia's military resurgence.

Tensions have been rising in Sweden and the rest of the Baltic region amid signs of more assertive Russian behaviour, including Russian planes regularly skirting or violating the national air space of neighbouring countries.

And in October 2014, Sweden launched a massive hunt for a foreign submarine, suspected to be Russian, in the Stockholm archipelago over an eight-day period.

The military subsequently confirmed that "a mini submarine" had violated its territorial waters, but was never able to establish the vessel's nationality.

US think tank Cepa in June published a report claiming Russia had held exercises with 33,000 troops aimed at practising an invasion of the Swedish island of Gotland in the Baltic Sea, among other sites, on March 21-25.

Swedish security experts have widely downplayed the risk of a possible invasion, instead interpreting the exercises as a sign of increased posturing from Moscow.