Hungary, whose government maintains support of Russian narratives over war in Ukraine, is accused of seeking defence data.
Ukraine has detained two people who it accuses of spying for Hungarian military intelligence.
The SBU security service claimed in a statement on Friday that the former members of the Ukrainian military were recruited by Hungary to conduct “espionage activities to the detriment of our state”. Relations between Kyiv and Budapest have long been strained, but the antipathy has grown amid Russia’s invasion of Ukraine.
The Ukrainian intelligence agency said that the pair had been recruited by a handler in Hungarian military intelligence to gather information about defence systems in the country’s west, host to a significant Hungarian diaspora.
There was no immediate response from the Hungarian government.
The SBU said the two suspects, a 40-year-old man and a woman, had been placed in custody and given notice that they were under suspicion of committing treason. They both now face up to life in prison, it added.
The pair was allegedly given cash and special equipment for secret communication and tasked with passing on details about air defence batteries and other military capabilities in the western Zakarpattia region bordering Hungary.
The SBU alleged the man had tried to recruit at least two people as informants.
It added that this was the first time in the history of Ukraine that a Hungarian spy network had been found to be working against Kyiv’s interests.
Throughout the Ukraine war, Hungarian Prime Minister Viktor Orban has delayed Western military aid to Kyiv and maintained warm relations with Russian President Vladimir Putin, at odds with his European Union peers.
Orban has used staunch nationalism to build his political base at home, in particular stressing grievances over the territories lost to neighbouring states – including Ukraine – under the Versailles Treaty that ended World War I.
Budapest has berated Kyiv for years, claiming discriminatory actions against the 150,000 or so ethnic Hungarians, most of whom live in the Zakarpattia region.
The SBU noted that the suspected agents had also been tasked with studying “the socio-political views of local residents, in particular, scenarios of their behaviour if Hungarian troops entered the region”.