Romania on Friday sparked fury in Moscow by blocking a Moldova-bound plane carrying a senior Russian minister entering its airspace because of an EU travel ban over the Ukraine crisis.
The foreign ministry in Bucharest confirmed to AFP that the passenger jet carrying deputy prime minister Dmitry Rogozin was "not allowed to fly over Romanian airspace".
The commercial liner, heading to Moldova's capital Chisinau with some 160 passengers on board, was forced to turn around and land in the Belarusian capital Minsk instead.
Bucharest acknowledged that the decision was made because of EU sanctions introduced in 2014 as the conflict surged between pro-Russian rebels and government forces in eastern Ukraine.
Rogozin is among dozens of Russian and Ukrainian individuals to have been hit by the punitive measures, which include asset freezes and travel bans.
He has been targeted for his role in the Russian annexation of Crimea in March 2014.
After arriving in Minsk, the minister vented his anger at Romania's decision, saying the blockade was an unprecedented move.
"We have flown with the airline company several times before and never had any problems... with Belarusian, Polish, Slovakian and Hungarian airspace," Rogozin told the Russian Interfax news agency.
He later tweeted: "Expect a response, scoundrels!"
Russia's foreign minister summoned Romania's envoy to Moscow to "express a decisive protest" over the move.
"Moscow considers this incident to be a conscious provocation that causes serious harm to our bilateral relations," the ministry said in a statement.
Rogozin had been on his way to Moldova, which is currently locked in a tug-of-war between the pro-Western government and Kremlin-friendly figurehead President Igor Dodon.
Dodon slammed the move to block Rogozin as an "unprecedented Russophobic show" aimed at undermining Moldova's "good relations with our strategic partner Russia."
"This script is written not in Chisinau but in the West," he said.
The small country wedged between Romania and Ukraine has an East-West cultural, linguistic and political split.
Earlier this month, Moldovan lawmakers issued a fresh demand for Russia to pull out troops stationed in the breakaway territory of Transdniestr since a ceasefire deal halted a bitter conflict 25 years ago.
In May, Chisinau kicked out five Russian diplomats which saw Moscow turf out its officials in revenge.