A separatist group has seized control of an oil-rich region in southern Yemen, shattering a relative calm in the country’s stalemated civil war – a significant move in a country located along a key international trade route that also threatens to bring new risks to the Persian Gulf region.

The secessionist Southern Transitional Council, STC, a group backed by the United Arab Emirates, this month seized most of the the provinces of Hadramout and Mahra, including oil facilities.

Yemen has been mired for more than a decade in a civil war that involves a complex interplay of sectarian grievances and the involvement of regional powers.

Watch moreYemeni voices: First-hand accounts of the war

TheIran-aligned Houthis control the most populous regions of the country, including the capital Sanaa. Meanwhile, a loose regional coalition of powers – including Saudi Arabia and the UAE – has backed the internationally recognised government in the south.

The war has created a humanitarian crisis and shattered the economy. Still, since 2022, violence has gradually declined as the sides reached something of a stalemate in the war.

The move by the UAE-backed separatists upends the political arrangement among the anti-Houthi partners.

The war in Yemen began in 2014, when the Houthis marched from their northern stronghold of Saada. They took the capital, Sanaa, and forced the internationally recognised government into exile. Saudi Arabia and the UAE entered the war the following year in an attempt to restore the government.

The new fighting pits the STC against the forces of the internationally recognised government and its allied tribes, even as they are both members of the camp fighting against the Houthi rebels in the country’s broader civil war.

The STC is the most powerful group in southern Yemen, with crucial financial and military support from the UAE. It was established in April 2017 as an umbrella organisation for groups that seek to restore South Yemen as an independent state, as it was between 1967 and 1990.

The latest moves reinforced the STC positions across southern Yemen, which could give them leverage in any future talks to settle the Yemen conflict. The STC has long demanded that any settlement should give southern Yemen the right of self-determination.

The STC enjoys loyalty through much of southern Yemen. It is chaired by Aidarous al-Zubaidi, who is also vice president of the country’s Presidential Leadership Council, the ruling organ of the internationally recognised government.

The STC and other UAE-supported groups now control most of the southern half of Yemen, including crucial port cities and islands.

The other party in the latest fighting includes the Yemeni military, which reports to the internationally recognised government. They are allied with the Hadramout Tribal Alliance, a local tribal coalition supported by Saudi Arabia.

These forces are centered in Yemen’s largest province of Hadramout, which stretches from the Gulf of Aden in the south to the border with Saudi Arabia in the north. The oil-rich province is a major source of fuel for the southern areas of Yemen.

Earlier this month, STC forces marched to Hadramout and took control of the province’s major facilities, including PetroMasila, Yemen’s largest oil company, after brief clashes with government forces and their tribal allies.

This took place after the Saudi-backed Hadramout Tribal Alliance seized the PetroMasila oil facility in late November to pressure the government to agree to its demands for a bigger share of oil revenues and the improvement of services for Hadramout’s residents.

The STC apparently seized on this move as a pretext for wrestling control of Hadramout and its oil facilities for itself and expanding areas under its control in Yemen.

STC forces then marched to the province of Mahra on the borders with Oman and took control of a border crossing between the two countries. In Aden, the UAE-backed force also seized the presidential palace, which serves as the seat of the ruling Presidential Council.

Saudi troops also withdrew earlier this month from bases in Aden, a Yemeni government official said. The withdrawal was part of a Saudi “repositioning strategy", said the official who spoke on condition of anonymity to discuss the matter.

Saudi Arabia sent a delegation to Harramout to meet with the province’s governor and other political and tribal leaders in efforts to tamp down tensions.

Maj. Gen. Mohammed al-Qahtani, the Saudi delegation’s chairman, said in video comments that his government “rejects any attempts to impose a fait accompli", in Hadramout.

The escalation shattered the relative quiet in Yemen’s war, which has been stalemated in recent years after the Houthis reached a deal with Saudi Arabia that stopped their attacks on the kingdom in return for ceasing the Saudi-led strikes on their territories.

Watch moreYemen’s uprising, 10 years on: Half the population risks starvation

Ahmed Nagi, a senior Yemen analyst at the International Crisis Group, said Saudi Arabia appeared “deeply dissatisfied” with the STC’s latest move.

“The group has gone beyond the Saudi-led arrangements,” he said. “The UAE seems to be the main winner, expanding its influence in the Yemeni crisis.”

The United Arab Emirates, meanwhile, insisted that its approach was in line with Saudi Arabia’s goal of "supporting a political process” to settle the multi-layer conflict in Yemen.

It said the country’s governance and territorial integrity is “an issue that must be determined by the Yemeni parties themselves".

(FRANCE 24 with AP)