MANILA, Philippines — Davao City Mayor Rodrigo "Rody" Duterte on Sunday warned perpetrators of the "tanim-bala," or bullet-planting, scheme that he would let them swallow bullets as punishment.

“I don't have the ambition to become the president, but if I am the president, I will let you swallow those bullets even if it means death," Duterte said in Cebuano during his weekly television program "Gikan sa Masa, Para sa Masa" aired on Sunday.

The tough-talking mayor was reacting to the growing number of incidents where passengers are accused of bringing bullets in their luggage while claiming innocence. The extortion ploy has been dubbed "tanim bala" or "laglag bala."

On Friday, engineer Augusto Dagan was also accused of bringing bullets to the airport after authorities discovered two 9-millimeter bullets in his luggage at the Davao International Airport.

READ: Engineer nabbed for bullets in luggage

Dagan was reportedly traveling to Davao to have an ocular inspection for the ongoing project of the Davao City Water District.

Duterte described this incident "incredible" and said the engineer's case should be thoroughly investigated, as innocent people have been deemed victims of the scheme. Duterte noted said similar incidents have been reported in the past two years.

"You better stop it but I know that the PNP (Philippine National Police) is conducting (an) investigation," the mayor said.

Duterte claimed that a syndicate, including airport employees, might be behind the extortion scheme against passengers.

"'Yung mga empleyado in cahoots with the police," Duterte said. "This is what really makes up our country, pera-pera lang sa droga, protektado sa lahat."

The mayor added that in Manila, even the police are being bribed.

"That's why we have so much trouble here now... if it's here in Davao then I will kill you. If I'd become a president then you will be over," Duterte said in Cebuano.

"I will order your execution within 24 hours," he added.

Duterte, known for his hardline stance against crime, has been tagged by international rights organizations to have a hand in human rights violations in Davao City.

President Benigno Aquino III, meanwhile, has ordered an investigation into the bullet-planting issue and check the Ninoy Aquino National Airport for possible traces of the syndicate behind the scheme.

"Kung talagang may sindikato diyan, titingnan po ng ating kalihim na si Secretary Jun Abaya," Presidential Spokesperson Edwin Lacierda said on Saturday.