Southern Transitional Council forces advanced earlier this month into the eastern provinces of Hadhramaut and Al Mahra

UN Secretary General Antonio Guterres warned on Wednesday that Yemen is at risk of sliding back into full-scale conflict after advances by southern separatists, and he urged all sides to exercise restraint to avoid reigniting a civil war that has been largely dormant in recent years.

Mr Guterres said that forces affiliated with the Southern Transitional Council advanced this month into the eastern provinces of Hadhramaut and Al Mahra, moves he said threaten to deepen divisions and derail fragile efforts towards peace.

The STC, part of Yemen’s UN-backed government, launched military operations to take over three provinces with the avowed aim of combating terrorism and smuggling. It accuses other parties in the government of mishandling the economy and national security.

“As I told the Security Council, unilateral actions will not clear a path to peace,” Mr Guterres said. “They deepen divisions, harden positions and raise the risk of wider escalation and further fragmentation.”

He warned that a renewed conflict would have serious implications beyond Yemen’s borders, including for security in the Red Sea, the Gulf of Aden and the Horn of Africa.

The UN chief called on all parties to de-escalate tension and resolve disputes through dialogue, stressing that Yemen’s sovereignty and territorial integrity must be preserved.

Mr Guterres, who recently returned from visits to Saudi Arabia and Oman, also condemned the continued detention of 59 UN staff and partner personnel by Houthi authorities, demanding their immediate and unconditional release.

“In recent days, Houthi de facto authorities referred three of our colleagues to a special criminal court. This referral must be rescinded. They have been charged in relation to their performance of UN official duties. These charges must be dropped,” he said.

The UN has repeatedly rejected Iran backed Houthi accusations that its staff or operations in Yemen were involved in spying.

“We must be allowed to perform our work without interference,” Mr Guterres said. “Despite these challenges, we remain committed to providing life-saving support to millions of people across Yemen.”