The prosecutor at the International Criminal Court Thursday (ICC) launched initial probes into alleged crimes against humanity during the "war on drugs" in the Philippines and political upheaval in Venezuela.
"Since 2016, I have closely followed the situations" in both the Philippines and Venezuela, prosecutor Fatou Bensouda said in a statement.
After "a careful, independent and impartial review... I have decided to open a preliminary examination into each situation."
In the Philippines, her office would "analyse crimes allegedly committed... since at least 1 July 2016, in the context of the 'war on drugs' campaign" launched by Philippine President Rodrigo Duterte.
"Specifically, it has been alleged that since 1 July 2016, thousands of persons have been killed for reasons related to their alleged involvement in illegal drug use or dealing," Bensouda said.
Many were allegedly "extra-judicial killings" carried out during "police anti-drug operations."
The ICC was opened in 2002 to prosecute the world's worst crimes.
The Philippines probe will be its first preliminary examination in a Southeast Asian nation.
In Venezuela, Bensouda said her office would probe crimes allegedly committed during demonstrations and political unrest since April 2017 against the government of President Nicolas Maduro.
"In particular, it has been alleged that state security forces frequently used excessive force to disperse and put down demonstrations, and arrested and detained thousands of actual or perceived members of the opposition," she said.
It will be only the second preliminary examination by the ICC in South America. One is under way in Colombia into alleged war crimes and crimes against humanity during the conflict with the FARC rebels.
Manila had been informed earlier that the ICC probe was to be opened and Duterte denied all charges of mass murder and crimes against humanity, his spokesman said.
"We view of course this decision of the prosecutor as a waste of time and resources," spokesman Harry Roque said, adding that Duterte merely employed "lawful use of force" against threats to the state and its citizens.
Duterte won a landslide victory in the 2016 elections largely on a pledge to kill tens of thousands of criminals and eradicate drugs in Philippine society.
He has since overseen a crackdown that has left nearly 4,000 drug suspects dead at the hands of the police. The authorities are also investigating more than 2,000 other cases of "drug-related" killings by unknown suspects.
Rights groups have put the total number of drug war deaths as at least twice the official figure, many of them committed by shadowy vigilantes.