Malaysia Airlines flight MH17 had been operating 1,000ft above the upper limit of closed airspace at the time of its disappearance over eastern Ukraine.
Pan-European air navigation service Eurocontrol states that the aircraft was flying at 33,000ft when radar contact was lost.
It states that the route had been closed by Ukrainian authorities up to 32,000ft.
But the route was "open at the level at which [MH17] was flying", says Eurocontrol.
In the wake of the loss of the Boeing 777-200ER, apparently with no survivors, the Ukrainian authorities have extended the restrictions within the Dnipropetrovsk flight information region, the airspace in which the jet was travelling.
Eurocontrol says the upper airspace closure limit has been withdrawn and that this closes all routes in the Dnipropetrovsk airspace.
"All flight plans that are filed using these routes are now being rejected," says Eurocontrol. "The routes will remain closed until further notice."
European authorities have activated their aviation crisis co-ordination cell in response to the 777 crash and the airspace closure.
"We call for an immediate and thorough investigation into the causes of the crash," says European Commission president Jose Manuel Barroso. "The facts and responsibilities need to be established as quickly as possible."
NATO secretary general Anders Fogh Rasmussen says: "Much is unclear about the circumstances of the crash. However, the instability in the region, caused by Russian-backed separatists, has created an increasingly dangerous situation.
"It is important that a full international investigation should be launched immediately, without any hindrance, to establish the facts and that those who may be responsible are swiftly brought to justice."