Stockholm (AFP) - Sweden is stepping up its military capabilities and exercises with NATO amid concerns over Russia's military resurgence, Defence Minister Peter Hultqvist said on Friday.

"It's a general fact that Russia is carrying out bigger, more complex, and in some cases more provocative and defiant, exercises. We are following that development and are now strengthening our military capability and our international cooperation," Hultqvist told paper of reference Dagens Nyheter.

Sweden, a non-NATO country which has a longstanding tradition of military non-alliance, will increase its exercises with the Alliance, including those on Swedish territory.

Swedish troops will take part in a large NATO exercise in Spain in September, and in Norway in 2018.

The country also took part in NATO's recently completed Baltops exercises in the Baltic Sea.

"We need to keep up with the new reality. It is broadly anchored in parliament that it is important for the United States to be militarily represented in Europe and this is part of the balance," he said.

His comments came a day after US think tank Cepa 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.

Sweden's defence budget has been cut back drastically since the end of the Cold War, as the military turned its focus away from territorial defence in favour of international peacekeeping missions.

But a June 16 defence ministry proposal to parliament refers, for the first time since the end of the Cold War, to building up the country's defence "to prepare Sweden for war".

In April, Sweden announced plans to raise defence spending by 10.2 billion kronor (1.09 billion euros, $1.18 billion) for 2016-2020, mostly to modernise ships to detect and intercept submarines.

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The re-positioning comes amid an uptick in Russian military activity in the past year.

In October, a week-long search for a suspected Russian submarine in waters off Stockholm was called off, with the military unable to identify the intruding vessel.

A series of alleged airspace violations by Russian jets over the last year has also raised jitters in Sweden.

Swedish public opinion has long been opposed to NATO membership, though recent polls have shown an increase in support.