An explosive device hidden at a Petah Tikva junior high school was discovered late Tuesday and defused, police said, adding that the charge was ready for use.

Two men were arrested, including the Brenner junior high school custodian, 31, who is believed to have ties to organized crime, according to central district commander Bruno Stein.

However, the school’s principal denied the school custodian had been arrested or had any connection to the case, Army Radio reported.

Stein said the second man had ties to the custodian and more arrests were expected.

Law enforcement officials said the two were suspected of selling drugs and firearms on school property. The investigation is ongoing.

The bomb was discovered after a special police unit received information that criminal elements were expecting to take delivery of an explosive device and that it had been deposited at the school, Ynet reported.

A large force of police and bomb disposal squads swept through the school during the evening to search for explosive devices, finding the bomb in the school’s gym.

“The quick action of the unit prevented a real danger to the pupils and staff at the school who did not know that there was a bomb in the school while they were there,” the police said in statement.

Petah Tikva is one of several central Israel towns to have suffered a wave of underworld bombings over the last several months, thought to be assassination attempts between warring crime families.

In February, two people were killed when a bomb exploded in their car in the city, and later that month, the car of the deputy mayor was bombed. He was unhurt. An assailant also tossed a grenade into an open air market in the city in late February, injuring five.

This is not the first time a school has been used to store bombs.

In February a kindergarten teacher in Nahariya found components of an explosive device in a sandbox at her school.

A week earlier, Northern District police discovered an extensive weapons arsenal hidden in a school and other places in the Galilee village of Abu Sinan.

Rockets, grenades, explosives, detonators, RPGs and hundreds of bullets were concealed in several locations in the village, including in a kindergarten and a drainage ditch.