(Geneva) The heads of six UN agencies and three NGOs called on Thursday for the immediate and unconditional release of their staff detained by Yemen’s Iran-backed Houthi rebels.  

“Aid workers, human rights defenders and development specialists must stop being targeted in Yemen. All those detained must be immediately released,” they said in a joint statement.  

“We, the heads of relevant UN entities and international NGOs, call for the immediate and unconditional release of all personnel detained in Yemen by the Houthi authorities,” the joint statement said.

“We are extremely concerned by the recent detention by the Houthi authorities of 17 members of our organizations and many others associated with civil society organizations, national and international NGOs and other organizations supporting humanitarian activities.” , the text continues.

The declaration was signed by the heads of UN agencies responsible for health, food, human rights, development, culture and children.

It was also signed by the heads of Oxfam International, CARE and Save the Children International.

UN human rights chief Volker Turk said Tuesday that 13 UN staff members had been arrested, including six of his own staff.  

“These arrests are unprecedented, not only in Yemen but around the world. They directly hinder our ability to help the most vulnerable people in Yemen, including the 18.2 million people in need of humanitarian assistance and protection,” it added.  

The United Nations and humanitarian organizations said last week that the arrests of the personnel appeared to be the result of a coordinated operation.

The Houthis claimed to have stopped “a US-Israeli spy ring” operating under the cover of humanitarian organizations, a claim Mr Turk called “scandalous”.

The Houthi rebels are engaged in a civil war that has caused one of the world’s worst humanitarian crises. More than half the population depends on humanitarian aid in the poorest country on the Arabian Peninsula.

Rebels took control of the capital Sanaa in September 2014, prompting a Saudi-led military intervention on behalf of the Yemeni government in March 2015.

The NGO Human Rights Watch estimates that the Houthis have kidnapped and tortured hundreds of civilians since the start of the conflict.