A United Nations-chartered plane carrying 50 wounded Houthi rebel fighters on Monday left Yemen's rebel-held capital Sanaa for Omani capital Muscat for treatment, a Xinhua photographer witnessed.

The flight also carried 50 accompanying persons and three Yemeni doctors, a Houthi official told Xinhua.

Earlier the day, Turki al-Maliki, spokesman of the coalition forces, said in a press conference in Riyadh that the move came upon a "request" of the UN Special Envoy to Yemen Martin Griffiths "to facilitate the evacuation of the injured to Muscat for humanitarian reasons."

"The facilitation comes within the confidence-building framework between the Yemeni parties to prepare for the upcoming peace talks in Sweden," al-Maliki said.

The plane took off just few hours after Griffiths arrived in Sanaa.

Griffiths' office in Jordanian capital Amman told Xinhua by phone that the talks in Sweden would likely start in next few days.

"The UN envoy was expected to accompany Houthi rebel delegation from Sanaa to Sweden. But there was no exact information about the next movements of Griffiths," his office said.

The apparent breakthrough would pave the way for the upcoming negotiations in Stockholm.

Meanwhile, Houthi negotiating delegation has received guarantees from the UN for a safe depart and return to Sanaa, a Houthi official said on anonymity.

Saudi Arabia is leading the Arab military coalition that intervened in Yemen in March 2015 to support the government of President Abd-Rabbu Mansour Hadi after the Houthi rebels forced him into exile.