Malaysia Airlines says the route for Flight MH17 over the Ukraine had been accepted by Eurocontrol for an altitude of 35,000 ft. but Ukrainian controllers kept the 777-200ER (9M-MRD) flying at 33,000 ft. instead.

Despite the difference in altitude, the aircraft was in airspace that had been deemed safe to fly in by both the International Civil Aviation Organization (ICAO) and International Air Transport Association (IATA), according to the airline’s most recent statements on its website and on Twitter.

A block of airspace around the Crimea region more than 100 nm south of MH17’s southeasterly flight path from Amsterdam to Kuala Lumpur had been off-limits since April, although a progression of individual routes through the region had been restricted by Notice to Airmen (Notam) publication issued by the Moscow office in the hours and days before MH17 was downed on the afternoon of July 17 by a surface-to-air missile in the disputed eastern border of the Ukraine with Russia where Russian separatists are fighting the Ukrainian military. Officials have not yet determined who fired the missile or where it originated. All 283 passengers and 15 crew were killed.

In recent weeks, Ukraine has said separatist rebels have shot down a number of military aircraft, including an IL-76 airlifter, an Su-25 fighter and an AN-26 military transport.

Restrictions linked to MH17’s particular route allowed only flights flying higher than 32,000 ft., a restriction put in place “due to combat actions on the territory of the Ukraine near the border with the Russian Federation”, according to the Notam. Eurocontrol confirmed that the route was open above 32,000 ft., as did IATA.

The Notam goes on to say that the restrictions were to ensure international flight safety due to the “facts of firing from the territory of the Ukraine towards the territory of the Russian Federation”.

ICAO says “it is always the responsibility” of member states to issue warnings or airspace and ceiling restrictions “based on what they consider to be potential threats to civilian air services in the airspace under their sovereign control”, says a spokesman.  “ICAO does issue these warnings under extraordinary circumstances, for instance where States may not be able to due to command and control breakdowns, or possibly where a State does not have good diplomatic relations with the States who need to receive the safety advisory and it asks ICAO to do contact these adjacent States on its behalf.”

The route over Ukrainian airspace where the incident occurred “is commonly used for Europe to Asia flights,” says Malaysia Airlines. “A flight from a different carrier was on the same route at the time of the MH17 incident, as were a number of other flights from other carriers in the days and weeks before.”

After the shoot down, Ukrainian air service provider, Uksatse, closed air routes in the Dnipropetrovsk flight information region covering the eastern portion of the country.

Investigators are converging on the scene, with the U.S. sending experts from the Federal Bureau of Investigation and NTSB.

Eurocontrol says it is rejecting all flight plans that include the routes, adding that the European Aviation Crisis Coordination Cell (EACCC) “is being activated to coordinate the response to the impact of the airspace closure.” EACCC was established by the European Commission and Eurocontrol in 2010 to manage crisis responses for the European air traffic management network.

On its web site, Uksatse, says the crash was “the result of the terrorist attack against international civil aviation”.