UNITED NATIONS (AP) — Secretary-General Ban Ki-moon said Wednesday that widespread violence and turmoil in the past year have taken a toll on United Nations worker with 33 detained and one missing. Two contractors have also been abducted.

The U.N. chief, in a message on the International Day of Solidarity with Detained and Missing Staff Members, called for the immediate release of all those unlawfully detained. He also called on governments "to do everything in their power to prevent the taking of U.N. personnel."

Ban said that 33 U.N. workers were detained by government authorities in 15 countries as of March 15, including South Sudan where a World Food Program staffer was seized at an airport last October and several others were detained last year. In Syria, he said, numerous staff members from the U.N. agency helping Palestinian refugees have been detained and arrested or are missing.

"Abductions of United Nations personnel are increasingly carried out by unscrupulous actors seeking to extract ransom, make a political point, or impede the organization's operations," Ban said.

Ian Richard, vice president of the U.N. Staff Management Committee, said "every day that goes by is one too many for our abducted colleagues."

According to the secretary-general's latest report, 17 U.N. personnel were abducted and 138 were arrested and detained in 2013. Richard said nearly 90 percent of those detained or arrested by state authorities that year were locally recruited.

The international day marks the anniversary of the 1985 kidnapping in Beirut of former journalist and U.N. staff member Alec Collett who worked for the Palestinian refugee agency. His remains were found in 2009.