ADEN, Yemen－Yemen's main southern separatist group has announced it will establish self-rule in areas under its control, which the Saudi-backed government warned would have "catastrophic consequences".

The move threatens to renew conflict between the Southern Transitional Council, or the STC, and the Saudi-backed government, nominal allies in Yemen's war, even as the United Nations is trying to secure a nationwide truce to confront the novel coronavirus.

In a statement on Sunday the STC announced emergency rule in Aden and all southern governorates, saying it would take control of Aden's port and airport and other state institutions such as the central bank. The Saudi-backed government and southern regions of Shabwa, Hadhramout and Socotra, among the few areas under coalition control, issued separate statements rejecting the declaration.

Yemen's Foreign Minister Mohammed Al-Hadhrami said the STC announcement constituted "a resumption of its armed insurgency" and a "rejection and complete withdrawal from the Riyadh agreement", a deal that ended a previous standoff between the separatists and the government last year.

The STC "will bear alone the dangerous and catastrophic consequences for such an announcement", Al-Hadhrami said.

The conflict, seen as a proxy war between Saudi Arabia and Iran, has been in a military stalemate for years.

The Houthis hold most major cities despite fighting that has killed more than 100,000 people. The war has choked supply lines in the poorest Arabian peninsula country, leaving millions of people on the brink of famine and dependent on international aid.

The Saudi-led coalition has announced a unilateral ceasefire prompted by a UN plea to focus on the coronavirus pandemic. It extended the ceasefire on Friday for a month, but the Houthis rebel have not accepted the truce and violence has continued.

While Yemen has reported only one confirmed case of the novel coronavirus, aid groups fear a catastrophic outbreak should it spread in a country with a shattered health system and little testing.

The UN is trying to convene virtual talks to forge a permanent truce, coordinate coronavirus efforts and agree on humanitarian and economic confidence-building measures to restart peace negotiations stalled since late 2018.

The STC, which has said it wants to be included in any political negotiations, in January pulled out of committees implementing the Riyadh deal.

AGENCIES VIA XINHUA