"I can tell you that Kubis has tendered his resignation and the Secretary-General has accepted it with regret," said Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres.

"The Secretary-General is working on an appropriate replacement. We are all fully aware of the electoral calendar and are working as quickly as possible to ensure continuity of leadership," Dujarric told a daily press briefing.

Kubis is not leaving his post immediately and is expected to brief the Security Council on the situation in Libya on Wednesday, said the spokesman, who refused to say how long the envoy will stay.

"I would also add that we have a strong presence on the ground in Libya and all of our colleagues will continue, as they have done, working with Libyan institutions in light of the upcoming elections, not to mention the humanitarian challenges that the Libyan people face," said Dujarric.

"We are working expeditiously to fill the leadership, to fill the post to ensure continuity. But I think it's important to state that the support of the UN for the Libyan people, the support of the UN for the electoral process and in our technical capacity is continuing unabated," he said.

Dujarric said the resignation of Kubis did not come as a complete surprise to the Secretary-General, without giving details.

He said there was no disagreement between Kubis and the secretary-general ahead of the resignation.

The post of special envoy was created by Security Council Resolution 2542 of September 2020.

The resolution splits the original single leadership position of a special representative into two: a special envoy who exercises overall leadership of the UN Support Mission in Libya (UNSMIL) with a particular focus on good offices and mediation with Libyan and international actors to end the conflict, and a coordinator who is in charge of the day-to-day operations and management of UNSMIL.

The special envoy is based in Geneva and the coordinator in Libya.

By the time of the adoption of Resolution 2542, the position of UNSMIL leadership had been vacant for six months following the sudden resignation of Ghassan Salame as special representative for Libya.

Guterres' proposal to appoint then UN special coordinator for the Middle East peace process, Nickolay Mladenov, as special envoy for Libya won the support of the Security Council members in mid-December 2020.

But Mladenov announced his resignation from the world body in a surprise move in the following week, making him no longer eligible for the new position.

Guterres in January 2021 appointed Kubis of Slovakia as his special envoy for Libya.

In September, the Security Council twice failed to extend the mandate of UNSMIL for a substantial period of time as a result of differences among council members on the restructuring of UNSMIL to its original leadership position of one special representative, as well as language on the withdrawal of foreign forces and mercenaries from Libya.

The Security Council adopted a resolution on September 15 to approve a technical rollover till September 30 to allow more time for negotiations after the original draft resolution for a one-year extension would certainly fail.

Again on September 30, the Council had to approve another technical rollover as members could not find consensus on a substantive mandate renewal.

Resolution 2599 of September 30 decides to extend the mandate of UNSMIL till January 31, 2022, to allow the mission to work through the December 24 elections.