Bulgaria said on Tuesday it was sticking to its candidate for the top U.N. job, Irina Bokova, for now, after speculation that it was considering switching to backing EU commissioner Kristalina Georgieva.

Prime minister Boiko Borisov said he would think what to do if Bokova did not come first or second in the next round of voting for U.N. Secretary General, due on Sept. 26.

But he did not spell out whether that meant he would consider another candidate, and said he would not let other countries interfere in Bulgaria's decision.

That appeared to be a rebuff to senior diplomats and officials who told journalists over the weekend that Bulgaria was considering Georgieva, a power figure responsible for sorting out the bloc's budget after Britain's vote to leave the EU.

Speculation mounted after Russia's foreign ministry said German Chancellor Angel Merkel had been pushing for a different Bulgarian candidate in the race to lead the international body. Berlin later said it had not interfered in the process.

"We have sought support ... and we will continue to do so until Sept. 26. Everyone should put utmost effort, me included, for Mrs Bokova to be among the first two candidates," Borisov told reporters.

"But there is no way after 26 if she is not first or second, to continue with that topic and then we all we should decide how to proceed," Borisov said.

South Korea's Ban Ki-moon will step down from the top U.N. job at the end of the year and former Portuguese prime minister Antonio Guterres, who also served as the U.N. High Commissioner for Refugees, has been the front runner so far.

Bokova, who has served as Bulgarian ambassador in France and Monaco and was an acting foreign minister between Nov 1996-Feb 1997 in a Socialist government, polled equal third among 10 contenders in the last U.N. Security Council secret ballot. A senior Bulgarian government official called her performance so far "unconvincing".