DUBAI/GENEVA (Reuters) - Saudi Arabia released seven prisoners it was holding from Yemen’s Houthi movement, who were flown to the Houthi-controlled capital Sanaa on Wednesday by the Red Cross, the day after a Saudi prisoner freed by the Houthis arrived in Riyadh.

The apparent swap comes as Yemen’s warring parties are still hammering out details of a larger prisoner exchange that they agreed last month as a confidence-building gesture at the first major peace talks of the nearly four-year-old war.

The U.N. special envoy to Yemen, Martin Griffiths, welcomed the release and said he hoped it would encourage the rapid implementation of the larger prisoner swap.

“The [special envoy] is very encouraged by this positive spirit from the two parties,” his office said on Twitter.

The war pits the Iran-aligned Houthis who control the capital Sanaa and most population centers against a government now based in the southern port of Aden, backed by forces from Arab states.

The International Committee of the Red Cross, which provided the planes for both the freed Saudi and the seven freed Yemenis, said in a statement it had acted as a neutral intermediary and was not involved in negotiations over the releases.

“We are delighted these persons will soon be home,” Yahia Alibi, head of the ICRC Regional delegation in Kuwait, said in a statement. “We stand ready to act as a neutral intermediary so that thousands more affected by this conflict can return to their families.”

The United Nations is pushing for the warring parties to carry out the agreed prisoner exchange and implement a ceasefire in the main port city of Hodeidah to pave the way for a second round of discussions to end a war in which tens of thousands of people have been killed.