Russia is the main international security threat to Sweden, and foreign enemies may try to exploit an elevated risk of extremist violence from Islamists and the far right, the Swedish security service said on Wednesday.

"We must all learn to live with the serious security situation," Charlotte von Essen, head of the security service, told a news conference, unveiling an annual report into threats facing the country which abandoned centuries of neutrality and applied to join NATO since Russia invaded Ukraine.

"Above all Russia, but also China and Iran continue to constitute the biggest threat to Sweden and they are working and to a certain extent also working together to change the current security system," she said.

Last August, the agency raised its terrorism threat level assessment to 4 from 3 on a scale of 5, after several incidents in which individuals in Sweden and neighbouring countries burned Korans, outraging Muslims and triggering jihadist threats.

In a statement accompanying its report, the security service said threats from both the far right and Islamist groups could be stirred up or exploited by Sweden's enemies abroad.

"Foreign powers can use violent extremists and other types of organizations and individuals as proxies to conduct security-threatening activities deniably," it said.

The Security Service's head of operations, Fredrik Hallstrom, told the news conference that as increasing numbers of Russian spies had been expelled from the West, Moscow was changing its tactics and "using more opportunistic methods".

Sweden's NATO bid has yet to be approved by member state Hungary whose parliament may vote on it next week. Nordic neighbour Finland, which has a long border with Russia, joined last year. (Reporting by Anna Ringstrom and Stine Jacobsen Editing by Peter Graff)