Eleven Yemeni employees of United Nations agencies have been detained by Yemen's Houthi rebels under unclear circumstances, authorities said Friday, as the rebels face increasing financial pressure and airstrikes from a U.S.-led coalition. Others working for aid groups also have been taken, reports UNB.

The detentions come as the Houthis, who seized Yemen's capital nearly a decade ago and have been fighting a Saudi-led coalition since shortly after, have been targeting shipping throughout the Red Sea corridor over the Israel-Hamas war in the Gaza Strip.

U.N. spokesman Stéphane Dujarric in New York acknowledged 11 U.N. staffers had been taken.

“We are very concerned about these developments, and we’re actively seeking clarification from the Houthi de facto authorities regarding the circumstances of these detentions and most importantly, to ensure the immediate access to those U.N. personnel," he told journalists. "So I can further tell you that we’re pursuing all available channels to secure the safe and unconditional release of all of them as rapidly as possible.”

Of the 11, the U.N. said nine are men and two are women. Six worked for the U.N.'s human rights agency, while one apiece worked for its special envoy's office, its development arm, UNICEF, the World Food Program and UNESCO.

The Mayyun Organization for Human Rights, which also reported U.N. staffers were held, named other aid groups whose employees were detained by the Houthis across four provinces that the Houthis hold — Amran, Hodeida, Saada and Saana.

“We condemn in the strongest terms this dangerous escalation, which constitutes a violation of the privileges and immunities of United Nations employees granted to them under international law, and we consider it to be oppressive, totalitarian, blackmailing practices to obtain political and economic gains,” the organization said in a statement.

Save the Children, told the AP that it was “concerned of the whereabouts of one of our staff members in Yemen and doing everything we can to ensure his safety and well-being.” The group declined to elaborate.

CARE International also said one of its staffers had been detained without being given a reason.

Bd-pratidin English/Tanvir Raihan