In a statement, the SBU said it had detained two suspected agents who, it said, were being run by Hungarian military intelligence.
There was no immediate response to a request for comment from the Hungarian government.
However, relations between the two countries have often been fraught. Hungarian Prime Minister Viktor Orban has been sceptical about Western military aid for Ukraine.
The SBU said the two suspects are former members of the Ukrainian military, adding they are in custody, and have been given notice they are under suspicion of committing state treason.
The SBU added the agents were tasked with passing on to their handler details about Ukraine's air defence batteries, and other military capabilities in the Transcarpathia region of southern Ukraine, which borders Hungary.
Ukraine is home to around 150,000 ethnic Hungarians, most of them in the Transcarpathia region. Kyiv and Orban's government have clashed in the past over the rights of this community to use their native language.
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