"The only thing we can confirm is that we have information that a Swedish citizen may have been abducted against their will in Ukraine," said Fredrik Kärrholm at the National Criminal Investigation Department (Rikskriminalpolisen) to The Local on Monday.
Reports are circulating that the Swedish citizen may have been a mercenary soldier fighting on the Ukrainian government side but Kärrholm was unwilling to confirm any further details of the case.
"For security reasons, we don't comment further on any cases of this nature," he told The Local.
According to local news reports the man is in his sixties and was taken on July 20th at a checkpoint near Perevalsk in the Luhansk region. He remains in detention in the town of Horlivka, according to the Interfax news agency.
The news follows reports that two journalists from Swedish daily Dagens Nyheter (DN) were taken into detention by pro-Russian rebels on Sunday while reporting from the Malaysian Airlines crash site in eastern Ukraine.
The pair were taken to the SBU secret service building in the city where they were put in a room under guard. A further seven journalists joined them in the room, according to a DN report.
The Swedish journalists were able to send a text message to their editorial office and three hours later they were released.
The pressure is mounting from the EU and the US on Russian President Vladimir Putin to use his influence on the separatists in Donetsk and other areas of eastern Ukraine to allow unfettered access to the crash site and establish responsibility for the atrocity.
In a new blog post and Twitter comments on Monday, Swedish Foreign Minister Carl Bildt drew parallels with the shooting down of Korean Airlines flight 007 in 1983 by the Soviet Union.
"There are those who remember press conference where Soviet Ministry of Defence denied everything concerning shooting down of KAL007," he said.
Bildt warned that the the handling of the crisis would be consequences for EU policy towards Moscow.
"That this must have consequences for our overall policy on this issue is obvious. When we meet in the circle of EU foreign ministers in Brussels on Tuesday morning, this will quite obviously be one of the major issues," he said.