Muscat, Nov 20 : A UN special envoy has urged the immediate and unconditional release of all UN personnel held by Yemen's Houthi group during a visit to Oman, said his office in a statement.

During his visit, UN Special Envoy for Yemen, Hans Grundberg, held talks with senior Omani officials in the Omani capital, Muscat, on Wednesday (local time), focusing on recent developments in Yemen and efforts to revive a political process aimed at ending Yemen's decade of civil war.

He thanked Oman for its "steadfast support" for UN mediation efforts and stressed the need for coordinated regional and international backing to pave the way toward a political settlement in Yemen.

During talks with Mohammed Abdelsalam, the Houthi chief negotiator in Muscat, Grundberg called for the release of all the remaining UN staff "arbitrarily detained" by the Houthi group, reports Xinhua news agency.

In October, the United Nations secured the release of 12 UN foreign nationals in a mediation facilitated by Iran and Oman. The remaining detainees in Houthi prisons are Yemenis; although their precise number is unknown, sources estimate there are dozens.

The Houthis seized control of several northwestern Yemeni provinces in late 2014 when the civil war erupted, forcing the internationally recognised Yemeni government out of the capital Sanaa.

Meanwhile, in a separate development, the Houthi group has warned that it would resume missile and drone attacks against Israel if the ceasefire in Gaza collapses, according to a letter sent to the Palestinian Hamas movement.

The threat, broadcast by the Houthi-run al-Masirah TV channel on Sunday (local time), comes amid heightened regional tensions that could undermine the fragile US-brokered truce in Gaza, as well as renewed friction between Iran and the United States over stalled nuclear talks.

In the letter, the Houthis' newly appointed chief of staff, Yousif al-Madani, told Hamas, "We remain steadfast in our pledge and promise to stand with you, no matter the sacrifices."

Madani was appointed by the group last month to replace Mohammed Abdulkarim Al-Ghamari, who was killed along with dozens of Houthi officials in Israeli airstrikes on a building in Sanaa in August.

/IANS