The EU says Slovak authorities must explain how a block of explosives inadvertently ended up on an international flight after being planted in a passenger's luggage as part of a security test.

Spokesman Fabio Pirotta says the EU has demanded formal notification about the incident that occurred on Saturday, after a Slovak policeman slipped 3.4 ounces of explosive into the check-in luggage of an unsuspecting passenger at Poprad-Tatry Airport.

Slovak authorities say the exercise was part of the training for a bomb-sniffing dog. But police officers were later failed to remove the explosives, allowing it to travel undetected through airport security onto an aircraft bound for Dublin. On Tuesday, the Irish police detained the passenger, but released him soon after.

Pirotta says the EU Transport Commission only found out about it from the media.