The U.N. envoy to Yemen on Wednesday expressed optimism after meeting with the top leader of the Houthi rebels in a bid to end the country's devastating civil war.

In a statement issued before his departure from the rebel-held capital, Sanaa, Martin Griffiths said the rebels expressed a "strong desire for peace" and discussed "concrete ideas for achieving peace," without elaborating.

He said he may meet with President Abed Rabbo Mansour Hadi in the southern city of Aden.

A Saudi-led coalition allied with Hadi's internationally recognized government has been at war with the Houthis since 2015, and previous peace efforts have failed.

The U.N. hopes to prevent a full-scale coalition assault on the port city of Hodeida, a vital lifeline for a country already teetering on the brink of famine.

The government has called on the Houthis to withdraw from all the areas they control, including a "complete and unconditional" pullout from Hodeida.

The Houthis have refused to withdraw from Hodeida, but they recently offered to let the U.N. manage the port as part of a cease-fire in the city. Griffiths said earlier that both sides have agreed to the deal in principle, and that the U.N. would take over administration of the port as soon as they finalize the agreement.

The United Arab Emirates, a leading member of the coalition, has said operations in Hodeida have been paused to give the envoy a chance to broker a peaceful resolution. The fighting has largely been confined to the city's outskirts.

The U.N. considers Yemen to be the world's worst humanitarian crisis, with more than 22 million people in need of assistance.

Around 70 percent of Yemen's imported food and medicine arrives in Hodeida, and aid groups fear a protracted fight could shut down the port and potentially tip millions into starvation.

Houthis, accused by rivals of being an Iranian proxy, have arrested political opponents, including journalists.

The Yemeni Press Syndicate decried what it described as the abduction of Yemeni journalist Abdel-Salam al-Dais on Tuesday in Sanaa by an armed Houthi force. The syndicate held the group responsible and called for al-Dais' release.

In southern Yemen, where the UAE acts as de facto ruler through militias it has financed and armed, 29 detainees were released on Wednesday from Beir Ahmed prison in the southern city of Aden, according to two witnesses. They spoke on condition of anonymity because of security concerns.

An AP investigation last month exposed torture and sexual abuse rampant in prisons that sources say are run by the UAE, including Beir Ahmed.

Also on Wednesday, the mothers of detainees and men who have disappeared held a demonstration in front of Interior Minister Ahmed al-Maysari's house in Aden demanding the release of their sons, according to the relative of a detainee whose mother attended the meeting.

Al-Maysari said earlier that he has no control over the prisons.