MANILA - United Nations Special Rapporteur on Extrajudicial Executions Agnes Callamard said Wednesday that she welcomes media reports of the Philippine government's invitation for her visit the country and look into drug-related killings.

Callamard said on Twitter that she is waiting for the letter from the Philippine government and confirmation by official channels.

Presidential Spokesperson Ernesto Abella earlier said Wednesday that the Philippine government formally invited the UN rapporteur to investigate the thousands of killings during President Rodrigo Duterte's war on crime

"The Palace has sent the invitation to UN Special Rapporteur Agnes Callamard and is awaiting her response," Abella said during a press conference.

However, the U.N. official clarified that she has yet to receive the official invite.

Since July, Duterte has overseen a brutal crackdown on illegal drugs that has left more than 3,300 people dead, both at the hands of police as well as in unexplained circumstances, according to official data.

The United Nations, the European Union, the United States and international human rights groups have all raised concern over alleged extrajudicial killings.

In August, Callamard called out Duterte for endorsing the killing of drug suspects, describing the new president's statements as a "license to kill."

"Directives of this nature are irresponsible in the extreme and amount to incitement to violence and killing, a crime under international law. It is effectively a license to kill," Callamard warned.

"Intentional lethal use of force is only allowed when strictly unavoidable in order to protect life and should not be used for common policing objectives," she added.

Callamard's statements did not sit well with the president, prompting him to make a threat on pulling out the country from the United Nations. However, Duterte clarified that it was merely a joke.

Duterte last month challenged U.N. chief Ban Ki-moon and international human rights experts to visit the country, both to investigate the allegations and to face him in a public debate.

The government initially rebuffed Callamard when she announced plans to take up Duterte's challenge.

Callamard has since told AFP she would discuss with Manila the date and scope of her fact-finding mission, state guarantees for her freedom of movement and inquiry, and assurances about the safety of mission members and their interview subjects.

Abella said Wednesday the government also asked Callamard "to include in her investigation the killings of law enforcers by drug suspects so that she could obtain an accurate perspective of the drug problem in the country".

Amid growing criticisms from international observers, Duterte has rejected the allegations and called the campaign an internal affair of the Philippines.

In previous instances, the president dismissed what he considers intrusions into his governance.

UP political science assistant professor Jean Franco said that the UN's remarks should not be seen that way.

"Hindi naman exactly panghihimasok kasi when we ratify the treaty... sabihin nu'n, accountable tayo doon sa provisions ng treaty."

(It is not exactly intrusion because when we ratified the treaty, it meant that we should be accountable to its provisions.)

Franco added it might benefit the president to listen to constructive criticism and take an advice or two on how best to improve his governance. – With reports from Agence France-Presse and Mike Navallo, ABS-CBN News