The European air traffic regulator has confirmed the closure of eastern Ukrainian airspace "until further notice".
Eurocontrol said in a statement that all flight plans that use routes over this area are being rejected.
The announcement comes after Malaysia Airlines flight MH17 from Amsterdam to Kuala Lumpur crashed in eastern Ukraine killing all 283 passengers and 15 crew onboard.
Eurocontrol said in a statement: "Since the crash, the Ukrainian authorities have informed Eurocontrol of the closure of routes from the ground to unlimited (altitude) in eastern Ukraine.
"All flight plans that are filed using these routes are now being rejected by Eurocontrol. The routes will remain closed until further notice."
The European Cockpit Association (ECA), which represents more than 38,000 European pilots, said the route flown by the MH17 was "the most common route for flights from Europe to south-east Asia."
The UK Department of Transport has confirmed that "flights already airborne are being routed around the area by air traffic control in the region".
The US Federal Aviation Administration has said that all US flight operations over eastern Ukraine "will be suspended until further notice".
A number of European airlines have also confirmed that they will avoid flying through airspace near Russia's border with Ukraine.
German airline Lufthansa said it had decided to "fly a wide detour around east Ukrainian airspace with immediate effect". A spokesperson told the BBC: "The safety of our passengers is our top priority."
In March, South Korea's two major airlines — Korean Air Lines and Asiana Airlines — stopped flying over Ukraine airspace because of security concerns.
Flight MH17 had been due to enter Russian airspace when contact was lost.
Eurocontrol said the aircraft had been flying at Flight Level 330 (approximately 10,000 metres/33,000 feet) when it disappeared from the radar.