The Israel Prison Service has uncovered a sophisticated method of smuggling cellphones into Israeli jails, the agency announced on Sunday.

Security prisoners, the agency said, have been caught trying to smuggle miniature cellphones into prisons by swallowing them. The smugglers would commit petty crimes just so they could be arrested and then deliver the phones to a specific person already behind bars.

In other cases, phones were hidden within the prison walls.

These phones were used by inmates to direct terrorist acts. More than 70 smuggled cellphones have been seized thus far in 2019.

The IPS said it recently began installing jammers in prisons in order to ensure smuggled phones would be rendered unserviceable.

“The IPS is at the forefront of the war on terrorism,” the agency said in a statement.