The Malaysian Airlines Boeing 777 that disappeared at the weekend was carrying two passengers travelling on stolen passports, of whom one was a young man heading to Sweden, revealed the Aftonbladet newspaper on Tuesday.
"It's a man from Iran who was seeking asylum in Malmö," a Swedish relative of the man told the paper.
"I am completely certain that he was on the plane. No one has managed to get into contact with him since the accident."
The second man was on the way to Germany, police said.
The passports were Austrian and Italian, and were stolen in Asia several years ago.
The flight, which disappeared from radar screens on Saturday, was carrying 239 people. An extensive search effort is underway in the Gulf of Thailand.
Swedish police have filed a missing person report.
"Someone has reported that a distant relative was probably on the plane. We have compiled a missing person report and have sent it to Interpol, which will take over the matter," Torbjörn Edvinsson of the Gothenburg police told the paper.
Malaysian police told the BBC that the passenger travelling to Germany was "not likely to be a member of a terrorist group".