Days after the President of the Philippines, Rodrigo Duterte, caused controversy by reportedly calling President Obama a "son of a b****", he has returned with insults towards UN Secretary General Ban Ki-Moon.

President Obama cancelled his planned meeting with Duterte following his remarks, however, the two met informally at the ASEAN summit this week in Laos. The Filipino President has insisted that although he never used those words to describe the US President, he does think the Ban Ki-Moon is a fool to bring up human rights violations in the Philippines.

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According to Reuters, Duterte said: "Even Ban Ki-Moon weighed in. Also gave a statement before, several weeks ago, about the human rights violation. Sabi ko, isa ka pang tarantado (you are another fool)."

In August, President Duterte said that the Philippines might leave the UN after it called for an end to a surge in drug-related extrajudicial killings in the country. Duterte has refused to backtrack on his campaign against illegal drugs, despite international criticism, and turned down a meeting with Ban Ki-Moon at the summit in Laos.

Agnes Callamard, UN Special Rapporteur on summary executions, had said at the time: "It is effectively 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."

Earlier in the year, Ban Ki-Moon condemned the extrajudicial killings under Duterte, noting that they were "illegal and a breach of fundamental rights and freedoms".

Adding to data from police in the Philippines, at least 2,000 people have died in drug-related killings since Duterte came to power in May. While half of them have been killed during police operations, the rest have been killed in shootings by unidentified gunmen.

Duterte has been nicknamed The Punisher due to his tough stance against crime and threats to kill 100,000 criminals and "throw their bodies into Manila Bay". During his presidential campaign, he vowed to bring back capital punishment and give security forces the right to shoot to kill.