Philippine’s President Rodrigo Duterte has turned down a meeting with U.N. Secretary General Ban Ki-moon, the United Nations and the Philippine government said on Thursday.

A U.N. official said the request for a meeting was rejected because of a “scheduling incompatibility”.

Another U.N. official, who requested anonymity, said it was “basically unheard of” for a leader to be too busy to meet the secretary general.

Duterte had previously made threats to quit the body over criticism of his war on drugs.

U.N. chief Ban requested the bilateral meeting in Laos, which is hosting a summit of Association of Southeast Asian Nations (ASEAN) leaders next week, but officials from Duterte’s office said he could not fit it into his schedule.

“A meeting was requested but we could not agree on a time,” Ban’s spokesman Stephane Dujarric said.

Two U.N. human rights experts last week urged Manila to stop a wave of executions and killings that have escalated since Duterte won the presidency on a promise to wipe out drugs, drawing an angry response from Manila.

Philippine presidential spokesman Ernesto Abella confirmed Duterte would not be meeting Ban, but declined to comment on whether that was connected to his criticism of the U.N.

“Drug policy and human rights would have been top of the U.N.’s list at the meeting,” the official said.

Following the criticism of the surge in killings that has accompanied his anti-drugs campaign, Duterte railed against the United Nations in a news conference on Aug. 21, suggesting he might pull out and invite China and African nations to form an alternative global organization.

The following day his foreign minister, Perfecto Yasay, said the Philippines remained committed to the United Nations and would not be leaving, “despite our numerous frustrations with this international agency”.