The Houthi group, which seized power in Yemen in late 2014, released one of ministers from the ousted the government, TVs quoted the UN envoy as saying on Wednesday.
Abdulrazzak Al-Ashwal, former vocational training and technical education minister, was held several months ago along with other ministers and politicians within the Islah Party.
His release coincided with the ongoing visit of the UN envoy Ismail Ould Cheikh to the capital Sanaa.
In the past few days, Cheikh held talks with political factions within preparations for a new round of peace talks. The talks aim to end the ten-months armed conflict which has resulted in the worst humanitarian catastrophe in Yemen's modern history.
Since it seized power and expanded by force into most of the country's cities, the Houthi group has been detaining opponents including ministers and officials loyal to the government as well as reporters and activists.
Defense minister Mahmoud Al-Subaihi, who was arrested during the battles between the pro-government and Houthi forces for southern region, is still in custody.
Most of the detainees have taken into unknown places.
Lately, international organizations including the Human Rights Watch urged the Houthis to release all detainees and to allow access of families and monitors into sites of their detention.
One of the terms negotiated at UN-sponsored peace talks is to release all officials, reporters and activists held in connection with the current chaos.
Meanwhile, battles between the government and Houthi forces continued today in the provinces of Taiz, Baidha, Dhali, Jawf and Marib.
Sources said dozens of fighters from both sides have been killed and injured.
Moreover, civilians were killed and injured in shelling by the Houthis in Taiz, local sources said.
On the other hand, the Saudi-led coalition carried fresh airstrikes in the capital Sanaa and the provinces of Saada and Amran.
The coalition has been bombing Yemen since March in an effort to restore the legitimacy of the government.