The German government was told that civilian aircraft were in danger flying over the war zone in east Ukraine days before flight MH17 was shot down but did not inform airlines.

According to leaked diplomatic cables German authorities were told the situation in east Ukraine had become "very alarming" two days before the plane was downed on July 17, 2014, killing all 298 people on board.

The cables cite the downing of a Ukrainian air force plane at 20,000 ft, (6,000m) on July 14 as indicating cause for serious concern, reported German public TV channels NDR and WDR and Sueddeutsche Zeitung.

Surface-to-air-missiles able to hit aircraft at that altitude can also hit aircraft flying higher, experts told the broadcasters.

The Malaysia Airlines Boeing 777 had been flying at 10,000m (33,000 ft) when it was hit.

German intelligence had repeatedly warned of the threats to aviation in the area, according to the report.

However, a Lufthansa source told German media that the airliner had been given no warning of any change to the security situation in the area.

Lufthansa flew three airplanes over the war zone that day, including one 20 minutes before MH17 was hit.

"If the government had given our company a warning with an advisory of 'new status', then certainly Lufthansa would not have flown over eastern Ukraine any more," the source said.

Investigators are still trying to determine who is responsible for downing the flight, which was travelling from Amsterdam to Kuala Lumpar in Malaysia.

Dutch investigators are leading a probe into the cause of the crash.

The West and the Ukrainian government allege that MH17 was brought down by a BUK missile provided to pro-Moscow rebels by the Russian government.

The Kremlin denies the allegations.