BUDAPEST (Reuters) - A senior Ukrainian official has rejected calls for autonomy for ethnic Hungarians in western Ukraine made by Hungarian Prime Minister Viktor Orban, suggesting this would undermine the unity of the former Soviet republic.

Ukraine is already threatened by fragmentation due to a separatist revolt by Russian speakers in the country's east that erupted after protesters toppled Moscow-backed president Viktor Yanukovich in February.

Ukraine's deputy foreign minister told Hungarian newspaper Nepszabadsag in an interview published on Tuesday that minority languages would be treated equally to Ukrainian in education and official documents in regions with significant minorities.

"But cultural autonomy based on ethnicity... is not on the agenda," Natalia Galibarenko was quoted as saying. "We are a united state, we need to treat the concept of autonomy very carefully."

Referring to Orban's recent plea, Galibarenko said Ukraine's partners should refrain from statements which only play into the hands of Russia.

"Ukraine can be neither stable, nor democratic if it does not give its minorities, including Hungarians, their due," Orban said last month. "That is, dual (Hungarian) citizenship, collective rights and autonomy."

Orban, re-elected by a landslide win in April, reaffirmed a call for autonomy for 200,000 ethnic Hungarians in neighboring western Ukraine that he made as he was sworn in as premier.

His comments prompted Kiev to summon the Hungarian ambassador for an explanation and drew criticism from regional heavyweight Poland, an ally of Hungary within the Visegrad Four grouping of central European nations.

Orban has increased his popularity at home by voicing solidarity with ethnic Hungarians abroad, who were allowed to vote in a Hungarian election for the first time in April.

He has never suggested reuniting former, pre-1920 Hungarian territories - including what is now western Ukraine - with Hungary but his stance has offended governments in some neighbouring countries.

Orban has said autonomy could take many forms, but declined to go into more detail, adding it was up to ethnic Hungarians in Ukraine to decide what form of autonomy would be best for them.

(Reporting by Krisztina Than; Editing by Mark Heinrich)