Poland shuts down flights to Ukraine.

Darek Delmanowicz/PAP

Poland's LOT airline has cancelled all flights to Kyiv, Lviv and Odessa in Ukraine in connection with Russia's invasion of the country.

"No LOT planes fly over Ukraine and all transit flights will be flying alternative routes," LOT's spokesman Krzysztof Moczulski wrote on Twitter.

The European Union Aviation Safety Agency (EASA) on Thursday warned air operators of a high risk to civilian aircraft over Ukraine.

According to EASA, airspace and critical infrastructure, including airports, are exposed to military activities which result in safety risks for civil aircraft. It recommended that additionally, as a precautionary measure, operators should exercise extreme caution and avoid using the airspace within 100 nautical miles of the Belarusian- and Russia-Ukraine border.