Ukraine has declared a Hungarian consul persona non grata and demanded he leave the country within 72 hours.
The Foreign Ministry on October 4 accused the diplomat, who is based in the western Ukrainian town of Berehove near the Hungarian border, of "activities incompatible with the status of a consular officer."
The move comes after Kyiv accused Hungary's Consulate in Berehove of illegally issuing passports to ethnic Hungarians in Ukraine.
In response to Ukraine's decision, Hungarian Foreign Minister Peter Szijjarto told a press conference that his country was expelling a Ukrainian consul in Budapest.
Szijjarto also reiterated a threat to block Ukraine's accession to the European Union and NATO.
In a Facebook post, Ukrainian Foreign Minister Pavlo Klimkin warned on October 3 that "the events around the distribution of Hungarian citizenship in Berehove, let's say, do not add joy."
"They only complicate the already not perfect relationship between the two countries," he added.
In its statement, the Foreign Ministry expressed hope that the Hungarian side "will refrain from any unfriendly steps toward Ukraine in the future, and that its officials will not violate Ukrainian legislation."
It said that Kyiv considered Ukrainian citizens of Hungarian origin as a "unifying factor" in the two countries' relations, and called on Hungary "to do the same."
There are almost 200,000 ethnic Hungarians living in Ukraine's Zakarpattya region, where Berehove is located.
Speaking during a visit to Moscow, Szijjarto on October 3 accused Kyiv of "constantly" violating the rights of the country's Hungarian minority.
The expulsion is the latest in a series of diplomatic rows between Ukraine and Hungary, an EU and NATO member.
The latest tensions were triggered by a video that surfaced last month allegedly showing ethnic Hungarians being handed Hungarian passports in the consulate in Berehove.