Named as Pablo González by his lawyer, the freelance reporter worked for online media Publico and the La Sexta television channel.
“ABW agents have detained a Spanish citizen of Russian origin… He has been identified as an agent for the GRU” Russian military intelligence agency, Poland’s ABW agency said.
It accused González of “conducting his business for Russia while taking advantage of his journalist status”.
His lawyer Gonzalo Boye, known in Spain for representing Catalonia’s exiled former leader Carles Puigdemont, confirmed the charge late Thursday.
“Pablo Gonzalez is accused of an espionage offence… and is in temporary detention at the prison in Rzeszow” in southern Poland, he tweeted.
ABW said it detained Gonzalez on the night of February 27th to 28th in the southern border city of Przemysl where he had been for a couple of days.
“He was preparing to travel to Ukraine,” the agency said.
Before ABW’s announcement, media watchdogs expressed concern over the journalist’s situation.
Reporters Without Borders (RSF) tweeted Thursday that Gonzalez was detained for more than 72 hours “without any credible explanation”.
“He has had no access to his lawyer which is a denial of his fundamental rights,” RSF added.
The Committee to Protect Journalists (CPJ) called on Polish officials Tuesday to “immediately release” Gonzalez.
The CPJ said he had also been detained by Ukrainian agents in Kyiv on February 6th and accused of reporting from military-controlled areas in the eastern Donbas region without proper accreditation.
He was released without charge a few hours later.
Poland’s prosecutors said Gonzalez had been active in other countries and was carrying two passports and two Russian cards attributed to two different names.
If found guilty, he faces 10 years in prison.