
Since Russia began its invasion of Ukraine in late February, more than a dozen Air Serbia flights have been forced to return to Belgrade or Moscow due to bomb threats, and Belgrade airport has been evacuated at least three times.
"The foreign (intelligence) services of the two countries are doing so. One is an EU country and Ukraine is the other," Serbian President Alexander Vucic said.
In a statement, Oleg Nikolenko, a spokesman for Ukraine's Foreign Ministry, dismissed Vucic's comments as "baseless" and "untrue."
He also said Ukraine was disappointed with Serbia's refusal to join EU sanctions against Russia.
"We call on Belgrade to stand up for the truth and fully unite in support of Ukraine and preserve the values on which united democratic Europe is founded", the statement says.
Serbia, an EU membership candidate, is almost entirely dependent on Russian gas and oil. It refuses to impose sanctions against the Kremlin and holds regular flights to Moscow.
"We are continuing these flights literally out of principle, because we want to show that we are a free country and we make our decisions," Vucic said.
In recent weeks Belgrade has voted three times for UN resolutions condemning the Russian invasion of Ukraine and suspended it from the main UN human rights body. Moscow calls its actions in Ukraine a special military operation for the country's denazification.