Two pilot instructors were killed when a two-seater aircraft crashed during a training flight in Bulgaria on Friday, ahead of a military air show scheduled the next day, the prime minister said, Paralel.Az reports citing Reuters.

Acting Prime Minister Dimitar Glavchev arrived at the crash scene at the Graf Ignatievo air base in central Bulgaria.

The crash occurred at 12:30 (0930 GMT) and killed two pilot instructors, Defence Minister Atanas Zapryanov said.

The plane involved was an L-39ZA advanced training aircraft, the defence ministry said in a statement.

The ministry canceled the international air show planned to mark the 20th anniversary of Bulgaria’s admission to NATO on Saturday, and said an investigation of the accident was under way.