WARSAW, Poland – Three men have been caught red-handed in Poland while planting homemade explosives under two police cars in Warsaw, officials said Wednesday.

It’s the second case since Thursday in Poland of homemade explosives threatening public security. Poland is to host the NATO summit and a visit by Pope Francis in July.

Police spokesman Mariusz Mrozek said the men, aged between 17 and 35, were linked to anarchist groups. He says they have not confessed to having tried to destroy cars Monday night in a police parking lot in the Wlochy district.

The police were tipped that an attack was planned on a police station and caught the men as they were planting containers with flammable liquid and fuses under cars. Police experts who neutralized the explosives said they were capable of destroying the cars, according to Mrozek.

The men were put under three months’ arrest. If convicted of threatening public security, they could face up to eight years in prison.

Separately, a 22-year-old student confessed to leaving homemade explosives Thursday on a city bus in Wroclaw in the southwest. One person was slightly hurt when they exploded after the bus driver carried them out and into the street.

Mrozek said the police were working very intensively to assure the security of the top meetings in July.