Swedish prosecutors charged a man on Friday on suspicion of gun crimes and raising money for the outlawed Kurdistan Workers Party (PKK).
They said the case was the first time anyone had been charged in Sweden with attempting to provide finances to the PKK, designated a terrorist outfit by Türkiye, the European Union and the United States.
It comes at a sensitive time for relations with Türkiye.
"The investigation has given support for suspicions that the man was acting on behalf of the Kurdistan Workers Party," the prosecution authority said in a statement.
It said it was bringing charges against the man, who is in his 40s, as he was suspected of aggravated extortion, serious gun crime and attempted funding of terrorism.
The case comes as Ankara holds up Sweden's application for NATO membership, in part because it says Sweden harbors supporters of militant groups it considers to be terrorists.
Talks between the two countries over NATO accession are due to restart next week.
Sweden, which applied to join NATO last year following Russia's invasion of Ukraine, wants its membership ratified before the alliance's summit in mid-July in Vilnius.
Only Türkiye and Hungary have yet to approve the bid. Finland, which applied alongside Sweden and was initially blocked by Ankara, joined NATO in April.
Sweden says it has fulfilled all the conditions of a three-way pact with Türkiye and Finland struck in Madrid in June last year to smooth the path to NATO membership.
