The maker of the Airbus A400M military transport plane that crashed in Spain this month is warning air forces flying the plane to carry out checks on the aircraft's electronic systems before the next flights.

Airbus Defence & Space says it sent the so-called Alert Operator Transmission notice to all operators of the giant turboprop airlifter on Tuesday.

The cause of the crash that killed two pilots and two flight test engineers on May 9 near the city of Seville remains under investigation.

Four of the five countries that already have A400Ms — Britain, Germany, Malaysia and Turkey — grounded the plane after the crash. France, which has six, says it will only use the aircraft in urgent operations.