Slovakia's prime minister has apologised after saying he would hand over a Ukrainian region to Russia in exchange for COVID-19 vaccines.
On Monday, Slovakia became the second EU member after Hungary to receive doses of Russia's Sputnik V, even though it has not been approved for use in the EU.
During an interview with a local radio station, Igor Matovic was asked what he had promised Moscow for delivery of Russia's vaccines.
"Ukrainian Zakarapattia," he replied, the Ukrainian name of the western Transcarpathia region that borders Slovakia.
The comments drew a strong response from Ukraine, who summoned Slovak chargé d'affaires to protest and demand an apology.
The Ukrainian foreign ministry added in a statement that the comments were "unacceptable".
"Regardless of the motives, genre, or context, the statements of the head of the Slovak government, which directly affect the territorial integrity of Ukraine, are categorically unacceptable," the ministry said in a statement.
"[The comments] negatively affect the friendly and good-neighbourly atmosphere of Ukrainian-Slovak relations."
Matovic apologised for his remarks on Thursday, tweeting in Ukrainian; "Slovakia is your friend".
"Slovakia’s position on Ukraine’s territorial integrity has always been very clear. Respect for international law is a must," Matovic said.
"Apologies to all Ukrainians for my inappropriate reaction which could undermine their just efforts."
"I am all the more sorry that just a few days ago we had a very good conversation in Kyiv," Matovic added on Facebook.
Slovakia's foreign minister Ivan Korcok, who visited Ukraine in February, said he had also apologised to his Ukrainian counterpart Dmytro Kuleba.
In a separate tweet on Wednesday, Kuleba responded that Slovakia should offer to exchange several of its own regions for Sputnik V doses.
"Jokes" about territorial integrity are an especially sensitive issue for Ukraine after Russia annexed its Crimea peninsula in 2014. Moscow has also been accused of backing armed separatists in eastern Ukraine in a conflict that has claimed more than 13,000 lives.
The European Union and the United States have issued sanctions against Russia over the annexation
"The inappropriate words of the head of the Slovak government are at odds with Slovakia's consistent position in support of Ukraine's sovereignty and territorial integrity within its internationally recognised borders," added Ukraine's foreign ministry.
Ukraine banned the Russian vaccine in February and has only received 500,000 doses of the AstraZeneca jab.