"We can confirm that this person was detained over spying allegations," Ramunas Matonis, spokesman for the Police Department, told BNS.
A court has sanctioned the man's arrest for two months, he said.
The ongoing pre-trial investigation launched in cooperation with the State Security Department is being carried out by officers of the Lithuanian Criminal Police Bureau and is being led by the Vilnius Regional Prosecutor's Office, Matonis said.
"We cannot provide any more detail for now as we don’t want to undermine the investigation," he said.
The independent Belarusian TV channel Belsat reports that law enforcement authorities suspect Danielius of having infiltrated Belarusian organizations in Lithuania and passed information about them to Belarusian intelligence.
Danielius would introduce himself as a business consultant, and he would give lectures and offer legal assistance, the TV channels claims, adding that the man helped the Belarusian organizations Our House and Dapamoga.