"Bulgaria’s position is completely irrational and offensive to the Macedonians and our entire nation," Prime Minister Zoran Zaev said in a video address on Wednesday.
North Macedonia's prime minister on Wednesday blasted Bulgaria's veto of the start of his country's membership talks with the European Union, saying the move shows "neither friendship nor brotherhood."
The EU on Tuesday warned Bulgaria that it risked undermining security in the Balkans and elsewhere in Europe if it continues blocking North Macedonia's membership negotiations with the bloc.
EU member Bulgaria insists North Macedonia formally recognise that its language has Bulgarian roots and stamp out what it says is anti-Bulgarian rhetoric in the country before it will lift its objections to the country joining the European Union.
EU leaders gave North Macedonia and neighbouring Albania the green light in March to begin accession talks, although no date was set for the start of negotiations.
"Bulgaria’s position is completely irrational and offensive to the Macedonians and our entire nation," Prime Minister Zoran Zaev said in a video address.
"In the 21st century, it is neither European nor democratic to tell another how to feel, how to self-determine. It is not European (manner) to write the history of another nation."
Zaev said the dispute touched the core of his country's national identity, which includes its language.
The prospect of EU membership has long been seen as an incentive driving democratic, political and economic reforms in the volatile Balkans.
North Macedonia, previously known as Macedonia, has been a candidate for EU membership since 2005, but a long-running dispute with Greece over the country’s name had blocked the process.
Greece had argued that use of the term "Macedonia" suggested claims on its own northern province of the same name, and usurped Greek history and culture.
The two neighbours struck a deal for the country to be renamed North Macedonia in exchange for Greece dropping its objections to EU membership.
The EU's current German presidency has been frustrated that another debate over history, this time with Bulgaria, has suddenly reared its head.
Zaev said North Macedonia remains "committed in seeking a solution" with Bulgaria.