UAE-backed separatists in southern Yemen have warned of an "imminent war" with Saudi-sponsored militants as divisions between the two sides continue to deepen.

In a statement, the so-called Southern Transitional Council (STC) said it had informed ambassadors of major countries to Yemen and the UN envoy Martin Griffiths that "the outbreak of war is imminent".

The group accused Riyadh-backed government of former Yemeni president Abd Rabbuh Mansur Hadi of violating a power-sharing settlement signed between the two sides last year.

The STC accused the former government of trying to regain control of southern provinces in violation of a "sustainable political agreement" reached last November.

The statement also said that Hadi's loyalists had attempted to overrun Aden, which was seized by the separatists last August.

Both the UAE-sponsored separatists and Saudi-backed militants loyal to Hadi serve a Riyadh-led military coalition which has been waging a bloody war on Yemeni people since March 2015.

Equipped and funded by the United Arab Emirates, the separatists have long sought southern Yemen to secede.

They had initially agreed to fight under the Saudi-led military coalition, but recently and after a decision by the UAE to effectively withdraw its forces from Yemen, the group has turned its weapons on rival militants loyal to Hadi.

The infighting has highlighted deepening divisions between Saudi Arabia and the UAE, the two countries that are leading the war on Yemen.

Ties between the two sides have soured over a number of issues, including what the Yemenis view as Abu Dhabi’s intention to occupy Socotra Island and gain dominance over major waterways in the region.

The threat of an imminent war comes in the wake of a unilateral ceasefire declared by Saudi Arabia earlier this month, citing the coronavirus outbreak.

Leading international weekly newspaper The Economist, however, raised doubts about the true objectives of the ceasefire on Saturday, saying Saudi Arabia was using the pandemic as a “fig leaf” for an exit from the Yemen "quagmire".

“Cynics doubt that compassion is truly motivating Saudi Arabia. For years its bombs have hit hospitals, houses and schools in Yemen—often, it seemed, on purpose," the London-based publication said.

“The Saudis want a way out and are using the coronavirus as a fig leaf,” it said, citing Yemeni Analyst Abdulghani al-Iryani.

According to the paper, “despite its vicious air campaign, Saudi Arabia has been unable to dislodge the Houthis from most of Yemen’s population centers, including the capital, Sana’a".

Its main ally, the United Arab Emirates, began scaling back its involvement in the war last year, The Economist said, adding in recent months they have held secret talks with the Houthis.

"Gone is the hope of returning Abd Rabbuh Mansour Hadi, the exiled Yemeni president, to Sana’a. Now the kingdom’s goal is to stop Houthi missile strikes on its own territory,” it added.

Griffiths said on Friday that ceasefire negotiations between Hadi and Houthis were nearing completion despite continuing military activities on several fronts.

"We are redoubling our efforts to bridge the outstanding differences between the parties," he said, adding he feared fighting would continue on the ground until an agreement was reached on the proposals.

The UN envoy said the city of Ma'rib east of the capital of Sana'a "remains the center of gravity of this war".

The US-based Armed Conflict Location and Event Data Project (ACLED), a nonprofit conflict-research organization, estimates that the Saudi war has claimed more than 100,000 lives in Yemen since 2015.

The UN says over 24 million Yemenis are now in dire need of humanitarian aid, including 10 million suffering from extreme levels of hunger.