WARSAW, Poland — Polish police say they have detained 21 people in connection with a false bomb threat that caused 800 people to be evacuated and four flights to be diverted from an airport near the capital.

The bomb threat occurred late Sunday and affected Warsaw’s Modlin Airport, which is north of the capital and serves budget airlines.

Dawid Marciniak, a police official, said Monday that police traced the hoax call to a party attended by 21 people, all of whom he said were drunk. Since nobody admitted to making the call, police detained them all.

He said whoever is found guilty could face a prison sentence ranging from six months to eight years and will also have to cover the financial costs of the security operation on Sunday.