Russia Friday said its passenger planes were banned by Kiev from entering two eastern Ukrainian cities, but pledged not to strike back.
"The Federal Agency for Air Transportation has been informed that starting from May 2, Ukrainian authorities have unilaterally banned Russian airlines from fulfilling flights to the airports of Donetsk and Kharkov," the agency said in a statement.
Calling the ban an "unprecedented" breach of international air service agreements, Moscow said the decision seriously violated passengers' rights and may cause a transport blockade in Ukraine's eastern regions, Xinhua reported.
Meanwhile, the agency said Moscow would not take any symmetrical measures, urging Kiev to refrain from any unfriendly steps.
The ban came the same day as Ukraine initiated a military assault in its eastern city of Slaviansk, trying to retake government buildings occupied by pro-Russia activists.
Ukraine's defence ministry has confirmed the loss of two helicopters. It said the aircraft were shot down by a surface-to-air missile, which proved the activists were not civilians but well-equipped and well-trained militants.
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The Kremlin said the assault meant Kiev had "crossed out" the Geneva agreements reached April 17.
Russia's foreign ministry also repeated its claim in a statement that "using the army against its own people is a crime and will lead Ukraine to a catastrophe".