Omani officials, accompanied by senior Houthi figures, arrived in Sanaa on Saturday to try to convince the rebels who control the capital to accept a ceasefire, Houthi sources said.
Yemen has been devastated by a civil war between the government – supported by a Saudi-led military coalition – and Iran-backed Houthi rebels since 2014. The country is on the brink of famine.
Diplomatic efforts to end the conflict have intensified in recent weeks.
"An Omani delegation arrived [in Sanaa], accompanied by Houthi spokesman Mohammed Abdul Salam and other [Houthi] officials," a rebel source told AFP on condition of anonymity.
The Saudi-led coalition controls Yemen's airspace and since 2016 had prevented Abdul Salam and other rebel figures from returning to Sanaa.
The delegation's arrival, which would have required approval from Riyadh, demonstrates a step forward in negotiations.
The Houthis have repeatedly demanded the reopening of Sanaa airport before any ceasefire agreement.
The source said the delegation would meet Houthi leader Abdulmalik Al Houthi and update him on talks held in Muscat.
The aim of the Omani mediators seems to be "to convince the Houthis to accept a ceasefire and take part in peace negotiations", the source added.
"We are working to advance arrangements on the humanitarian question as well as the peace process," Mr Abdul Salam told Houthi-run Al-Masirah television.
The visit aims to "complement efforts" made in Oman, he added.
The sultanate of Oman, which borders both Yemen and Saudi Arabia, is a close US ally but at the same time has good relations with Iran. It has regularly played the role of mediator in regional conflicts.
Muscat has hosted UN special envoy for Yemen Martin Griffiths and US envoy Tim Lenderking in recent weeks, while Iran's Foreign Minister Mohammad Javad Zarif met with Abdul Salam in Oman in late April.
On Monday Mr Griffiths urged rival Yemeni forces to "bridge the gap" to reach a ceasefire, following talks in Sanaa with Houthi officials.
"There's an extraordinary amount of diplomatic consensus … there is a real diplomatic energy now, which hasn't always been the case," Mr Griffiths said.
The effort to secure peace in Yemen comes after regional rivals Saudi Arabia and Iran restarted talks in April, holding their first high-level meeting since Riyadh cut diplomatic ties with Tehran in 2016.
The UN says Yemen is suffering the world's worst humanitarian crisis as its years-long war rumbles on, with tens of thousands killed, millions displaced and two-thirds of its 30-million population dependent on aid.
