(CNN) — The airspace over Ukraine and its border with Russia is empty, according to flight tracking websites, with heavy air traffic apparently avoiding the region as evening set in on Thursday, local time.
Images from ADS-B Exchange showed no aircraft over Ukraine, though the open-source site cannot display tracking data from aircraft operating in the area with the location broadcasting intentionally switched off.
Civilian flights over Ukraine, as well as Moldova to the south and parts of Russia, are currently restricted. One notice to pilots reads: "Air space of Ukraine closed for civil aviation flights due to military invasion of Russian Federation."
The European Union Aviation Safety Agency, or EASA, warned Thursday: "The presence and possible use of a wide range of ground and airborne warfare systems poses a HIGH risk for civil flights operating at all altitudes and flight levels.
The US Federal Aviation Administration said on Thursday that it was publishing an expanded notice to pilots that will "now cover the entire country of Ukraine, the entire country of Belarus and a western portion of Russia."
There are risks to flying over conflict zones -- as illustrated by the 2014 downing of Malaysia Airlines flight 17 over eastern Ukraine by a missile, killing 298 people.
Western officials and a Dutch-led investigation said Russian president Vladimir Putin bears responsibility for the incident; Putin denied it.