STOCKHOLM (Reuters) - Russia could try to influence the outcome of national elections in Sweden in September if authorities in Moscow feel their strategic interests are threatened, the Swedish security service said on Thursday.

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The service’s head of counter-intelligence, Daniel Stenling, cited membership of NATO - which Sweden has debated joining - and security around the Baltic Sea as two important issues for Russia.

“Russian espionage is still the biggest threat to Sweden,” he told an annual press briefing.

“We see that Russia has an intention to influence individual issues that are of strategic importance. If these issues become central in the election campaign, we can expect attempts at Russian influence.”

Stenling declined to say if his force had already seen evidence of such attempts.

Russia - which has faced accusations of trying to affect the outcome of voting in the United States, France and Germany - has repeatedly denied meddling in elections in the West.

On Tuesday, Latvia’s Ministry of Defence said accusations of money laundering at one bank and bribery allegations against the central bank governor could be part of a foreign campaign to influence elections due there in October. It did not name a specific country

Russia’s annexation of the Crimean peninsula in 2014 and support for separatists in eastern Ukraine has strained relations with the West and the Baltic region has become a flashpoint.

Sweden and other countries in the region have complained of repeated airspace violations by Russian military planes and Sweden has restationed troops on the strategically important island of Gotland in the Baltic Sea.

Sweden has held military drills with several NATO members and has debated joining the military alliance for years. The Kremlin has warned of unspecified consequences if it did.

The Social Democrats, the senior party in the current minority coalition government, have ruled out joining NATO.

The security service said Sweden’s decentralized, manual electoral system was difficult to manipulate, but the use of fake social media accounts and distribution of inaccurate news were also channels that could be used to influence opinion.

Prime Minister Stefan Lofven has, along with many European colleagues, previously voiced concerns about possible foreign meddling and Sweden has set up a”psychological defense” agency.