Sana’a, Asharq Al-Awsat—Violent clashes erupted in southwestern Yemen on Monday between Houthi insurgents and forces loyal to ex-president Ali Abdullah Saleh in what rebel sources said was the result of a dispute over oil supplies.

Other sources said the fighting started after the allies blamed each other for major losses they recently suffered at the hands of forces loyal to President Abd Rabbuh Mansur Hadi in the Al-Dalea governorate, 152 miles (245 kilometers) south of Sana’a.

“A bitter dispute arose between the Houthis and Saleh’s forces following the major losses in lives and ammunition they suffered in the Al-Dalea province on Saturday,” a Yemen source who preferred to remain anonymous told Asharq Al-Awsat.

Dozens of anti-Hadi militants were killed in Saturday’s fighting, including a senior commander of Yemen’s Republican Guard force as well as three other senior Houthi leaders.

Pro-Hadi fighters destroyed four armored vehicles and three tanks belonging to the Houthis and Saleh, the source said.

The dispute quickly escalated into violent clashes. It was unknown whether there were any casualties in the fighting, the source said.

After overrunning large parts of Sana’a last September, the Houthi movement forged an alliance with Saleh, who is still thought to be influential within the military establishment, despite stepping down from power in 2012. President Hadi and his Gulf backers accuse Saleh of facilitating the Houthi takeover of government facilities and military bases across Yemen.

Two Houthi fighters were killed on Sunday when their vehicle was destroyed by a landmine in Attaq, the provincial capital of the southern Shabwah governorate.

Eyewitnesses said they heard an explosion in the area which was quickly sealed off by the Houthi militants.

While no group has claimed the attack, sources from the city said the landmine had been likely planted by pro-Hadi forces.

Meanwhile, heavy clashes erupted on the outskirts of Aden on Monday between rebels and forces loyal to Hadi as the Houthis continued their shelling of the city’s residential areas.

Speaking to Asharq Al-Awsat, a senior Al-Hirak movement official said thousands of the Southern separatist group’s members are to be transferred to the port city of Aden in the south from an unidentified Arab state where they have undergone an intensive military training program.

Fouad Rashed, Secretary of the Supreme Council of the Al-Hirak movement, told Asharq Al-Awsat that a 5,000-strong military force will soon enter Aden to liberate the port city from Houthi insurgents. The force, the official said, will be backed by an equal number of local fighters.

“All indications confirm that this highly trained force, in addition to thousands of local fighters who will join it, will lead an operation to liberate Aden,” he said.

“I am very optimistic that the Southerners, for the first time after the invasion of their country in 1994, will perform this year’s Eid prayers with their country free from the Houthi militias and Saleh,” he added.

Yemen’s South used to be independent from the North until 1994 when Saleh captured Aden, prompting Southern leaders to flee abroad.

A supreme military command based in Aden will be leading the operations against the Houthis inside the city, the official said.

He added: “There have been promises from the coalition countries to provide the combatant force with heavy, advanced and effective weaponry.”

Saudi Arabia led an anti-Houthi coalition of ten Arab states, backed by Washington, in March in a bid to restore Hadi to power. President Hadi has been in exile in Riyadh since being forced to flee Aden following a Houthi advance on the southern port city in February.

Mohamed Ali Mohsen contributed reporting from Aden.