MANILA (AFP) -- Philippine President Rodrigo Duterte vowed Monday to press on with his drug war that has claimed thousands of lives, as he urged lawmakers to endorse "eye-for-an-eye" death penalties.

Duterte devoted large chunks of his annual State of the Nation Address to pushing his law-and-order policies that have made him hugely popular with many Filipinos but have been condemned by human rights groups and other critics.

"No matter how long it takes, the fight against illegal drugs will continue because that is the root cause of so much evil and so much suffering," Duterte told lawmakers from both houses of Congress.

"The fight will be... unrelenting despite international and local pressures. The fight will not stop until those who deal in it understand that they have to cease, they have to stop because the alternatives are either jail or hell."

Duterte swept to victory in last year's presidential elections after promising an unprecedented crackdown on drugs in which tens of thousands of people would die.

Since he took office on June 30 last year, police have reported killing nearly 3,200 people in the drug war.

More than 2,000 other people have been killed in drug-related crimes, according to police data. 

Rights groups say many of those victims have been killed by vigilante death squads linked to the government, and that Duterte may be overseeing a crime against humanity.

In a speech that lasted more than two hours, Duterte repeatedly hit back at his critics, including United Nation officials, ex-US president Barack Obama and prominent local media organisations.

Duterte on Monday also urged lawmakers to reintroduce the death penalty. 

"I ask congress to act on legislation to reimpose the death penalty on heinous crimes, especially illegal drug trafficking," Duterte said.

He said capital punishment was about "retribution" as much as deterrence.

"In the Philippines, it is really an eye for an eye, a tooth for a tooth. 

You took a life, you must pay it to die. That is the only way to get even."

The lower house of Congress this year passed a bill to bring back the death penalty for drug-related crimes, but the Senate has yet to approve it.

The death penalty was abolished in the Philippines in 2006 following a campaign by the influential Catholic Church.

Duterte also defended his decision last week to extend martial law across the southern region of Mindanao until the end of the year, to combat what he said was a rebellion by militants backed by the Islamic State group.

The militants have been occupying parts of the southern city of Marawi for more than two months, defying a US-backed military campaign that has claimed more than 600 lives.

"I declared martial law in Mindanao because I believed that was the fastest way to quell the rebellion at the least cost of lives and properties," Duterte told lawmakers.

On the foreign policy front, Duterte promoted his decision to pursue warmer relations with China despite a long-running row over rival claims to parts of the South China Sea.

Duterte thanked China for offering to fund infrastructure projects, and even build some bridges across the major river in Manila for free.

Critics of Duterte have said the president is sacrificing Philippine interests in return for short-term Chinese investment or aid. 

But Duterte insisted there were many long-term benefits to establishing closer ties with China as he repeated wide-ranging grievances against the United States, the Philippines' former colonial ruler and mutual defence partner.

"We cultivated warmer relations with China through bilateral dialogues, leading to the easing of tensions and improved negotiating environment on the West Philippine Sea," Duterte said, referring to the South China Sea by its local name.