The Doctors Without Borders (MSF) charity has “lost contact” with two of its foreign staff in Yemen, the group told AFP on Monday.
The employees, a German and a Burmese, had been in the northern province of Marib, the aid group said without giving further details.
International organizations and their staff have been periodically victimized by armed groups that have proliferated as a result of the country’s nine-year civil war.
In March 2022, two MSF employees were kidnapped in the southeast of the country, and released a few months later.
Al-Qaeda in the Arabian Peninsula (AQAP), considered by the United States to be the most dangerous branch of the network, freed five United Nations workers in early August. They had been held for a year and a half following their capture as they returned to the southern port city of Aden.
A month earlier, an employee of the UN World Food Program (WFP) was killed in an attack in the southern province of Taez.
After Iran-backed Houthi militia seized the Yemeni capital Sanaa from the internationally recognised government in 2014, Saudi Arabia mobilized a military coalition the following year in an effort to stop the rebel advance.
The fighting calmed markedly after a UN-brokered ceasefire that came into effect in April 2022 and has largely held even after the agreement lapsed last October.
According to the UN, the conflict in Yemen has killed hundreds of thousands of people and displaced millions.
It has also precipitated one of the world’s worst humanitarian crises, with two thirds of the population currently in need of humanitarian aid.