Five United Nations staff have been kidnapped in southern Yemen while returning to Aden after a field mission, the United Nations said .

The staff were kidnapped on Friday in the Governorate of Abyan, said Russell Geekie, spokesman for the top U.N. official in Yemen.

“The United Nations is in close contact with the authorities to secure their release,” Geekie said.

A Saudi-led military coalition has been fighting the Iran-aligned Houthi group in Yemen since 2015.

The coalition intervened in Yemen’s civil war in 2015 after the Houthis ousted the government from the capital, Sanaa. The conflict has killed tens of thousands of people and displaced millions, causing a dire humanitarian crisis.