Ukraine has alleged that Russian drones landed on Romanian territory during a series of strikes on a neighbouring Ukrainian city.
Foreign Minister Dmytro Kuleba told reporters after a news conference in Kyiv that Ukraine had photographic evidence supporting its claim.
However, Romania has rejected Kyiv’s version of events and BBC Verify says it cannot authenticate the image.
The row came as the Russian and Turkish leaders held talks.
Turkish President Recep Tayyip Erdogan had travelled to the Russian city of Sochi in an attempt to persuade President Vladimir Putin to revive the deal that allowed Ukraine to export grain safely through the Black Sea.
Mr Putin said the deal, which Moscow abandoned in July, would not be reinstated until the West met his demands for sanctions to be lifted on Russian agricultural produce.