Ukraine has long expressed unhappiness about the presence of Serbian volunteer fighters among the Russia-backed separatist forces it is battling in its eastern regions.
But Ukraine's ambassador to Serbia, Oleksandr Aleksandrovych, seriously ratcheted up tensions when he not only accused Russia of using its propaganda and security services to lure Serbians to fight against Kyiv, but hit close to Belgrade's heart by suggesting in an interview that Moscow was using Serbia to sow discord in the Balkans.
He rattled off a long list of alleged Russian destabilization efforts in his November 1 interview with the Balkan Investigative Reporting Network (BIRN): "Russia trains Serbian mercenaries to kill Ukrainians. Russia used Serbian extremists to make a coup d'etat in Montenegro. Russia encourages Serbian separatism in [the Serb-dominated Bosnian entity of] Republika Srpska to destabilize Bosnia and Herzegovina.... Russia uses the Serbian factor to destabilize Macedonia. Russia plays an active role in putting Serbian Kosovars against Albanian Kosovars. Russia sells its airplanes to Serbia to create tensions with Croatia."
The ambassador used those examples to highlight Kyiv's reasons to question Serbian intentions when it comes to their relationship.
"When you have Serbian politicians traveling to Crimea and praising Putin for his 'wise and strong policies', when you have Serbian mercenaries [fighting in separatist-held territories], when you have Serbia voting in the UN against Ukraine -- all of that naturally creates a negative image of Serbia in Ukraine," Aleksandrovych said.
Aside from Serbia's 2016 vote against a UN resolution calling for international monitoring of the human rights situation in Ukraine, Aleksandrovych's verbal volley referred to actions not officially endorsed by Belgrade: a trip to Crimea taken in early November by members of the opposition Radical Party, and, of course, the contentious Serbian volunteer fighters.
Aleksandrovych cited them as reasons to be wary of Serbia's cozy relations with Russia.
The Serbian Foreign Ministry did not react kindly to Aleksandroyvch's comments, warning Kyiv that it would be "forced to take steps" unless the diplomat corrected his "inadmissible behavior," and stressing that it was dedicated to building good relations with Ukraine.
In a statement, Serbian Foreign Minister Ivica Dacic reminded us that Serbia had taken a number of steps to prosecute its citizens who had fought abroad, including in Ukraine. And he sent his own zinger by noting that it was well known that Ukrainian mercenaries had taken part in "the crimes committed by Croatian forces against the Serb people in Croatia [during the 1990s], whom moreover Ukraine never officially condemned, unlike Serbia [in the case of Serbian fighters in Ukraine]."
That came after Aleksandrovych had been recalled to Kyiv for consultations -- officially to discuss the issue of Serbian mercenaries fighting on the side of pro-Russia separatists in Ukraine -- prompting Serbia's Foreign Ministry, in turn, to recall its ambassador to Ukraine for consultations.
Meanwhile, Ukrainian Foreign Minister Pavlo Klimkin called on Serbia to respect his country's sovereignty and territorial integrity.
Some 300 Serbs are said to be fighting in eastern Ukraine, some of whom were featured in a recent video produced by RFE/RL's Ukrainian Service.
The Serbian ultra-nationalist Radical Party called during a November 2 parliamentary session for Aleksandrovych to be expelled. It also stoked the growing dispute by announcing that two of its parliamentarians had visited Crimea at Russia's invitation, and had co-founded an international organization called "Friends of Crimea."
The Radicals made no bones about their support for Russian claims to the Ukrainian peninsula, which Russia seized in 2014, issuing a statement that the party "respects the territorial integrity of the Russian Federation with Crimea as its territory, as the Russian Federation respects the territorial integrity of Serbia."
Another group of Serbian politicians, including members of the Serbian People's Party, attended events in Crimea to mark the centenary of the 1917 Russian Revolution.
That led the Ukrainian Foreign Ministry to issue a statement in response expressing "serious concern about the illegal contacts by representatives of Serbia with occupied Crimea."
The Serbian government, rather than disavowing the actions of Radical and other opposition parliamentarians, chose to blame Ukraine for the breakdown in relations. Dacic described the ratcheting up of tensions as part of "an effort to wreck Serbia's relations with Russia."
On the other hand, members of some of the opposition parties in Serbia saw the situation as the outcome of an unsustainable foreign policy.
Aleksandra Jerkov, a member of the Serbian Democratic Party's foreign policy committee, has said that flip-flopping between support for Russia's and the EU's stance on Ukraine only makes Serbia seem like an unserious partner.
"We cannot simply switch sides depending on which way the wind is blowing, or based on what suits us at any given moment," she said.
"Serbia seems to be forgetting its own position as an aspiring EU member, and the fact that Europe expects us to align our foreign policy with that of the EU," Jerkov added.
Others, however, see ulterior motives in the current spat between Serbia and Ukraine.
According to University College London Professor Eric Gordy, "Ukraine wants to exert indirect pressure on Russia, and perhaps also to put some pressure on Belgrade over its close relations with Moscow. As for the Serbian side, I would characterize much of the current rhetoric as pre-election posturing [a reference to possible early parliamentary elections in 2018], and a desire by various parties to goad the EU [as a means of earning their nationalist spurs]."
Serbian President Aleksandar Vucic, who exerts control over domestic and foreign policy, would like to give the impression of staying above the fray and acting as the peacemaker.
"Ukrainians are a friendly people to the Serbs, and I am convinced that we will resolve this quickly. I would refrain from commenting on any individual statements; the Serbian institutions are doing their job. It's important to defuse tensions and maintain our friendly relations. I will do everything in my power to achieve that," said Vucic on November 9.
Difficult Balancing Act
Yet according to some observers the current crisis in relations with Ukraine is a direct consequence of Vucic's foreign policy -- trying to stay loyal to Moscow while maintaining good relations with the EU.
Vucic has a twofold aim in pursuing this approach, according to Aleksandar Popov, the director of the Novi Sad-based Center for Regionalism. "On the one hand, there is a desire to send a message to Progressive Party voters that we have an alternative to EU membership, but also a message to Brussels that we have a backup if the EU accession process is delayed. But this policy has its limits."
Speaking to the RFE/RL Balkan Service's Most (Bridge) program, Popov pointed out that Serbia has been warned recently that it cannot occupy two seats at the same time.
The warning came from U.S. Deputy Assistant Secretary for European and Eurasian Affairs, Hoyt Brian Yee, who said that Belgrade's balancing act between Moscow and the West was unsustainable.
In response, Serbian Defense Minister Aleksandar Vulin said that Yee's remarks represented "the greatest public pressure hitherto exerted on Serbia."
Vulin, whose pro-Russian stance is no secret, added that Serbia will pursue its course regardless of the demands of the "great powers."
Commenting on Vulin's statement, Popov is unconvinced by the bravado.
"In fact we've seen the anxiety that was caused by Hoyt Brian Yee's warning that Serbia cannot sit on both chairs at once. We were forced to look in the mirror, and were confronted by the reality that Vucic is not Josip Broz Tito, nor is Serbia the equivalent of the former Yugoslavia, and the international environment has changed. We will be in trouble when we are finally forced to choose -- EU or Russia."