"I can confirm that the Lithuanian prosecution service is carrying out a pre-trial investigation against the person in question and he is named a suspect in this pre-trial investigation," she said.
"Since we are speaking about private persons and a pre-trial investigation, which is now ongoing, the prosecution service cannot provide more information at this moment," Martinoniene said.
She also did not say whether a request would be sent to have Kucinskas extradited to Lithuania.
Russia's Alfa Banks is Kucinskas' biggest creditor.
Kucinskas was detained on July 15 as he was crossing the Slovenian-Croatian border.