This NOTAM apparently refers to the Russian takeover of the Crimea:
Reuters 03 Apr. 2014
(Reuters) - Europe's aviation safety authority warned on Thursday of "serious risks" for international airlines flying over Crimea because there may be two services managing airspace there after the region's annexation by Russia.
The European Aviation Safety Agency said Russia had published a series of notices saying it intended to provide air traffic services within the area controlled by the flight information center at Simferopol, Crimea's main airport.
EASA, which is based in Germany, therefore said national aviation authorities in Europe should encourage carriers to avoid the airspace over Crimea, which Russia seized from Ukraine last month, and use alternative routes.
"It is unsafe if more than one Air Traffic Service provider is in charge of one single Flight Information Region (FIR); no compromise can be made with the safety of the flying passengers," Patrick Ky, executive director at EASA, said.
Europe safety agency urges airlines to avoid Crimean airspace | Reuters
I could not find any NOTAM warning against overflying of the war theater, even after several aircraft had been shot down.