Berlin accused Moscow on Monday of falsely claiming Chancellor Angela Merkel had tried to pressure Bulgaria to select a new candidate to succeed UN chief Ban Ki-moon. German foreign ministry spokesman Martin Schaefer said a Russian official representative had "spread things that are objectively false", branding the move as "unfriendly".
On Sunday, Russian foreign ministry spokeswoman Maria Zakharova asserted that at this month's G20 summit, Moscow had indicated to Merkel in a "clear way" that "any direct or indirect attempt to influence (Bulgaria) was unacceptable".
The skirmish comes as Bulgaria has worked, according to some media, to change its candidate for the post of UN secretary general, which becomes vacant next year.
Bulgaria would replace UNESCO Director General Irina Bokova as its candidate with European Commission Vice President Kristalina Georgieva, according to these reports.
A spokesman for the EU executive declined to comment Monday on "speculation in the press".
Bulgarian Deputy Prime Minister Rumiana Bachvarova said Monday that Bokova's candidacy was "not sufficiently convincing" and that there would be "news in coming days" on the subject.
Ten candidates are running to succeed Ban, and the name of the next secretary-general could be announced in October at the earliest.