MANILA, Oct. 12 (Xinhua) -- The Philippines has sent an invitation to the United Nations rapporteur Agnes Callamard to probe the increasing number of drug-related killings in the country, a government spokesman said on Wednesday.

"Executive Secretary Salvador Medialdea said the palace has sent the invitation to the UN rapporteur Agnes Callamard and is awaiting her response," Presidential spokesperson Ernesto Abella told a news conference at the Malacanang presidential palace.

In the invitation, Abella said the "palace also urged - and I think it is notable - the UN rapporteur to include in her investigation the killing of law enforcers by drug suspects so she could obtain accurate perspective of the drug problem in the country."

He said the Philippine government is urging Callamard to also look into the killings of law enforcers who were also killed in the campaign to eradicate illicit drugs.

News reports said more than 3,000 suspects had been killed, some extrajudicially, in the fight against drugs since President Rodrigo Duterte took the presidency on June 30.

Duterte said there are at least 4 million Filipinos who are into drugs. He warned that if not eradicated, the Philippines will continue to be governed by narco-politicians.

The Philippine senate and the House of Representatives have conducted investigations into the drug menace.

The UN, US, European Union and other international human rights groups have criticized the Duterte administration for carrying out a bloody anti-drug campaign, prompting Duterte to lash at these critics.

Despite the intense criticisms, Duterte has vowed to continue his anti-drug campaign.

As of Oct. 10, the Philippine National Police said that a total of 1,550 suspected drug users and pushers have been killed since July 1. On the other hand, the police said at least 13 policemen and three soldiers were killed.

The police also said that close to 800,000 drugs suspects have "surrendered" since the campaign was launched.