Hungarian prosecutors are asking a court to keep in custody four men detained in connection with the deaths of 71 migrants found in a truck in neighboring Austria.

Prosecutors in Kecskemet said they would request the preliminary arrest of the three Bulgarians and an Afghan at a closed-doors hearing Saturday in the central Hungarian city.

The truck with 71 dead migrants was found Thursday in the safety lane of the main Budapest-to-Vienna highway. The suspects were detained in Hungary later that day.

It wasn't clear how long the bodies had been inside the truck, which Hungarian prosecutors said set off from Kecskemet. Austrian officials say one of the suspects owns the truck and two others apparently took turns driving.

Hundreds of thousands of migrants have arrived in Europe this year.