The firebrand leader referred to the martial law while speaking to businessmen in his home city of Davao on Saturday.

"If I wanted to, and it (the illegal drugs problem) will deteriorate into something really very virulent, I will declare martial law," said Duterte, who previously served as mayor of Davao.

"No one can stop me," he added, referring to the Supreme Court and Congress.

According to the constitution, the president can declare martial law for a maximum of 60 days, and only to stop an invasion or a rebellion. The parliament has the authority to revoke the measure within the first 48 hours, and the Supreme Court can review the legality of the move.

The issue is especially sensitive in the Philippines, where the one-time dictator Ferdinand Marcos imposed a period of martial law in 1972 and only lifted it in 1981. The 60-day limit was established in the 1987 Constitution, which was passed after Marcos' was ousted.

On Saturday, however, Duterte said he might ignore the regulations.

"The 60-day (limit) will be gone," he said. "And I'd tell you now, if I have to declare martial law, I will declare it - not about invasion, insurrection, not about danger. I will declare martial law to preserve my nation - period," he told the audience.

The 71-year-old Duterte boasted personally killing suspected criminals in Davao

Duterte changes tune on martial law

Duterte was voted into office in May, promising an unprecedented crackdown on illegal drugs. He has since waged a brutal and controversial war on organized crime, which has claimed some 6,000 lives, both in police raids and killings by suspected vigilantes.

While Manila's international partners repeatedly decried unchecked killings and called for more oversight, Duterte responded with insults and vowed to carry on until illegal drugs were eradicated.

Last month, Duterte himself rejected the idea of imposing martial law as "nonsense," but soon changed his position.

'Bomb them all'

Also on Saturday, Duterte addressed the problem with the Abu Sayyaf terror militia, which kidnapped dozens of foreigners and Filipino citizens after capturing their vessels at sea. Indonesia, Malaysia and the Philippines have all pledged to combat the problem together.

Duterte stated that Filipino forces had orders to target kidnappers regardless of hostages.

If the navy or the coastguard spot "kidnappers and they're trying to escape, bomb them all," he said.

"They say 'hostages.' Sorry, collateral damage," Duterte added, saying that the approach would allow security forces to crackdown on the militants.

He also advised potential victims to not "allow" themselves to be kidnapped.

dj/rc (AFP, AP, Reuters)