The Philippine government has formally invited a United Nations rights rapporteur to investigate the thousands of killings during President Rodrigo Duterte’s war on crime.

A presidential spokesman told reporters in Manila that the presidential palace has sent the invitation to UN Special Rapporteur Agnes Callamard and is awaiting her response.

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 extra judicial killings. The acid-tongued Duterte has rejected the allegations and called the campaign an internal affair of the Philippines.

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

Meanwhile, following a periodic review of the country’s commitments to the international body, the UN Committee on Economic, Social and Cultural Rights has expressed concern at Duterte’s drug war.