Hungary has summoned the Ukrainian ambassador after the Ukrainian Security Service (SBU) raided the offices of ethnic Hungarians.
The Hungarian Cultural Association in Transcarpathia said in a statement that SBU officers had raided the association's headquarters and the home of its chairman, searching for evidence of "activities aimed at violently changing the borders."
The association called on Ukrainian authorities to end what it called a "witch-hunt."
The SBU confirmed the raid and others in a statement on its website.
It said it conducted searches at local charitable foundations in the Transcarpathian region, checking "information about the involvement of the foreign fund in activities aimed at violating the state sovereignty of Ukraine."
Hungarian Foreign Minister Peter Szijjarto said on November 30 that Hungary had protested the raids at Ukraine's Foreign Ministry and added he would raise the issue at a meeting of NATO foreign ministers beginning on December 1.
The two countries have repeatedly clashed over what Hungary says are curbs on the rights of around 150,000 ethnic Hungarians living in Ukraine to use their native tongue, especially in education. Ukraine passed a law in 2017 restricting the use of minority languages in schools.
Last month Ukraine barred entry to two Hungarian government officials over what Kyiv called meddling in local elections, an accusation Hungary denied.
Szijjarto called it "unacceptable" that a country that wants to be part of the transatlantic community "continuously intimidates and puts pressure on a minority belonging to a NATO member."
Szijjarto made the comment in a video statement posted on his Facebook.
Hungary has repeatedly hinted at blocking Ukraine's membership of NATO.