An Air India plane took off for Ukraine on Thursday morning to bring back Indians from the eastern European nation, which is now facing a Russian offensive.
However, Ukraine said it had closed its airspace to civilian flights because of a "high risk" to safety, and Europe's aviation regulator also warned about the hazards of flying in bordering areas of Russia and Belarus because of military activities.
Ukraine State Air Traffic Services Enterprise said on its website that the country's airspace was closed to civilian flights starting at 00:45 GMT on Thursday and that air traffic services had been suspended.
The European Union Aviation Safety Agency (EASA) said airspace in Russia and Belarus within 100 nautical miles (185 km) of their borders with Ukraine could also pose safety risks to airlines.
The Air India flight AI 1947 started from the Indira Gandhi International Airport (IGIA) here at around 7.30 am for Boryspil International Airport in Kyiv.
The plane is expected to arrive there in nearly six hours, according to flight tracking website FlightAware.
Meanwhile, a Ukraine International Airlines flight from Kyiv landed at the Delhi airport at around 7.45 am on Thursday.
"There were 182 Indian nationals onboard the flight and majority of them were students... A couple of more flights have been scheduled," Anju Wariah, Director at STIC Group, said.
After weeks of rising tensions, Russia on Thursday announced a military operation against Ukraine.
The Ukrainian authorities issued a "notice to airmen", which stated that flights of civil aircraft within Ukraine "are restricted due to potential hazard for civil aviation".
Indian government officials said the decision regarding Air India's flight -- which is en route to Kyiv -- will be taken soon.
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