A Yemeni humanitarian worker whose detention highlighted the intimidation and torture of activists by Houthi rebels was freed on Saturday, the UN said.

Awfa Al Naami, the country manager for Saferworld, a UK-based organisation helping people in conflict zones, was summoned for questioning at the Houthi national security office in Sanaa on January 28 and had not been heard from since.

“The Special Envoy to Yemen, Martin Griffiths, urged Awfa’s release during his last trip to Sanaa where he met with Houthi leaders,” a UN official said . “She is now reunited with her family."

Yemeni lawyers and activists also campaigned for Ms Al Naami's release and have called for an end to the rebels' intimidation campaign.

“This is only a small part of what Yemen’s civil society is facing on the ground. This important space shrinking every day is what makes Yemen even darker,” said Radhya Almutawakel, co-founder of Mwatana Organisation for Human Rights, a Yemeni NGO.

Ms Al Naami's detention was only the latest in a series of atrocities committed by the Houthis, according to Amnesty International. Throughout the conflict in Yemen, human-rights defenders and journalists have been harassed, threatened, beaten, arbitrarily detained and forcibly disappeared, the rights group said.

Yemen’s former human rights minister Hooria Mashour welcomed Ms Al Naami's release and called for the rebels to free all detained activists.

"The Houthi should stop these crimes against innocent people," she said.

Ms Mashour said the rebels' detention of women went against the values of Yemeni society. "For the first time in Yemeni history we are seeing these crimes against women," she said.

Activists said this was not the first time Ms Al Naami had been interrogated, and that no reasons were given for her arrest.

“In recent months she has been subject to various threats and intimidation, as part of a larger, co-ordinated Houthi campaign against development and humanitarian workers in Yemen,” the Centre for Applied Research in Partnership with the Orient said.

The Iran-aligned rebels have been battling the government of President Abdrabu Mansur Hadi, which is backed by a Saudi-led military coalition.

Ms Al Naami was known for calling on the international community to intensify efforts to end nearly four years of civil war that has created what the UN calls the world’s largest humanitarian crisis.

“Peace means that no matter how much we disagree, we have to go into dialogue, I have to accept all your flaws and you have accept all my flaws,” she said last March.

Ms Al Naami’s release was welcomed by Yemeni activist Rasha Jarhum, founder and director of Peace Track Initiative and representative of the Women's Solidarity Network.

“To me her release is a symbol of the success of Yemen’s peace process. I am grateful and my hope is restored,” Ms Jarhum said on Twitter.

The development comes as Mr Griffiths tries to implement a prisoner swap deal between Yemen's warring sides, as part of efforts to build confidence in a slow-moving peace process. Both parties need to agree on the lists of prisoners to be swapped before any progress can be made.

The UN hopes the prisoner exchange and a truce in the main port city of Hodeidah will pave the way for a second round of peace talks.

A UN official confirmed to The National that Ms Al Naami's release was independent of the prisoner negotiations.

The prisoner swap was one of the least contentious confidence-building measures agreed upon at UN-sponsored peace negotiations in Sweden in December.

AFP.