MANILA - Presumptive president Rodrigo Duterte will revive debates on the re-imposition of capital punishment to deliver on his campaign promise to fight crime relentlessly, a close ally said Saturday.

Reviving the death penalty in the conservatively Catholic nation "will not be smooth sailing," but it it should be placed on legislators' agenda, said Senator Aquilino Pimentel, president of Duterte's PDP Laban party.

"I'm sure dito sa Duterte administration, babalik tayo sa debate sa re-imposition ng death penalty. Babalik tayo doon. In the meantime, meron tayong existing na batas, i-enforce na lang yun," he told DZMM.

"Wala na kasi natatakot. Under a President Duterte, matakot na sila," he said.

Former president Gloria Arroyo signed a law repealing capital punishment in 2006, just before she flew to the Vatican for an audience with Pope Benedict XVI and as she grappled with waning public support due to an election fraud scandal.

"Hindi po yan smooth sailing," Pimentel said of the possible death penalty discussions.

"Kasi kung magsu-survey ka sa mga senador diyan, hati-hati ang opinyon, wala pong unity diyan sa death penalty. At least, ma-agenda, mapapagusapan," he added.

Duterte has vowed a "bloody war" against criminals, particularly drug dealers, as he sought to bring to the entire country the anti-crime drive that he said, made Davao attractive to investors.

The tough-talking mayor will also seek a review of juvenile delinquency laws and push for the death penalty for drug-related crimes, Pimentel said.

Duterte will crack the whip on high-profile detainees who have turned their jail cells into extravagant dwellings, the senator said.

"Ang nangayri sa atin, the jailer has lost control of his or her jail," he said.

Successive raids on the national penitentiary since late 2014 have revealed that inmates have built bars and recording studios in jail. Some were even found to have been keeping inflatable sex dolls.