Manila - Authoritarian firebrand Rodrigo Duterte was sworn in as the Philippines' president on Thursday - and quickly launched a foul-mouthed vow to wipe out drug traffickers and even urged ordinary Filipinos to kill addicts.Duterte, 71, won last month's election in a landslide after a campaign dominated by threats to kill tens of thousands of criminals in a relentless war on crime, and tirades against the nation's elite that cast him as an incendiary, anti-establishment hero.After a measured speech after taking his oath before a small audience inside the presidential palace, the outspoken leader paid an evening visit to a Manila slum and unleashed profanity-laden threats against drug traffickers in front of a crowd of about 500 people"These sons of whores are destroying our children. I warn you, don't go into that, even if you're a policeman, because I will really kill you," the head of state told the audience."If you know of any addicts, go ahead and kill them yourself as getting their parents to do it would be too painful."Duterte has previously alleged some police officers were engaged in drug trafficking.Repeating a favourite campaign refrain, the new president also said it would make good business sense to set up funeral parlours."I assure you you won't go bankrupt. If your business slows I will tell the police, 'Do it faster to help the people earn money.'"In his speech earlier at the Malacanang presidential palace, as he took over from Benigno Aquino, Duterte had given notice there would indeed be dark days during his six years in office.Rough ride "The ride will be rough but come join me just the same," Duterte said in his remarks, which opened with familiar themes about the need to instil discipline in a graft-infested society."The problems that bedevil our country today which need to be addressed with urgency are corruption, both in the high and low echelons in government, criminality in the streets and the rampant sale of illegal drugs in all strata of Philippine society and the breakdown of law and order."Duterte, a lawyer who earned a reputation as an authoritarian figure as mayor of the southern city of Davao over most of the past two decades, said these problems were symptoms of eroding Filipino faith in their leaders.He had previously outlined a vision for his anti-crime programme that included reintroducing the death penalty, with hanging his preferred method of execution.He said he would issue shoot-to-kill orders to the security services and offer them bounties for the bodies of drug dealers. He also urged ordinary Filipinos to kill suspected criminals.During the campaign, Duterte said 100 000 people would die in his crackdown, with so many dead bodies dumped in Manila Bay that fish there would grow fat from feeding on them. He has been accused of links to vigilante death squads in Davao, which rights groups say have killed more than 1 000 people. Such groups are concerned that extrajudicial killings could spread across the Philippines under him, with a police crackdown following his election already leaving dozens of people dead.'I know what is legal'Duterte said at the presidential palace on Thursday his fight against crime would be "relentless and sustained", as he called on human rights monitors and critics in Congress to respect the mandate the Filipino people have given him.But he also insisted he would work within the boundaries of the law."As a lawyer and former prosecutor, I know the limits of the power and authority of the president. I know what is legal and what is not. My adherence to due process and rule of law is uncompromising," he said. Duterte also sought to portray himself as unifying figure."I was elected to the presidency to serve the entire country. I was not elected to serve the interest of any person or any group or any one class," Duterte said.During the election campaign, Duterte picked fights with the envoys of key allies the United States and Australia after they criticised his joke about wanting to rape a "beautiful" Australian missionary who was sexually assaulted and killed in a Davao prison riot.After his election win, Duterte also launched a seemingly unprovoked attack against the United Nations."Fuck you UN, you can't even solve the Middle East carnage... couldn't even lift a finger in Africa [with the] butchering [of] the black people. Shut up all of you," he said.On Thursday, Duterte offered a muted message of friendship to the international community."On the international front and community of nations, let me reiterate that the Republic of the Philippines will honour treaties and international obligations," he said.