ADEN, Yemen, Jul. 7 (Xinhua) - United Nations Special Envoy to Yemen, Hans Grundberg, issued an appeal Sunday for the immediate and unconditional release of UN staff, aid workers, and civil society members arbitrarily detained by the Houthi group in Sanaa.

The call comes on the heels of the latest round of prisoner exchange talks between the Yemeni government and the Houthi group, which concluded Saturday in Muscat, Oman, without making a reaching agreement.

However, parties of concerns agreed to hold a subsequent meeting to finalize the names of detainees to be released and how to arrange their release, which he said was "an important breakthrough."

Despite the positive progress, much more needs to be done, and faster for thousands of Yemenis to be reunited with their loved ones, he said, calling on relevant parties to continue working with his office to finalize the implementation plan for this understanding and to agree on more release operations.

The United Nations and the International Committee of the Red Cross have pushed for negotiations between the warring Yemeni sides aiming to address the ongoing humanitarian crisis surrounding prisoners in the conflict-ridden nation.

Grundberg reiterated the UN's demand for parties to refrain from arbitrarily detaining civilians and to respect Yemenis' rights under international law. He specifically emphasized the need for the immediate and unconditional release of UN personnel, aid workers, and civil society activists currently held in incommunicado detention in Sanaa.

Yemeni Minister of Human Rights and Legal Affairs, Ahmed Arman, has accused the Houthi group of detaining over 50 relief employees from international, UN, and local organizations in Sanaa since early June.

The Houthi group has controlled Sanaa and most of the northern Yemeni provinces since late 2014 and has since been engaged in a years-long military conflict with the Yemeni government forces.

The conflict has resulted in one of the world's worst humanitarian crises, according to the UN.