Somali National Army personnel climb into pickup trucks at Baidoua airport in Baidoa, Somalia, on November 9, 2022. [AFP]

Somali federal troops Monday entered the key city of Baidoa after clashes with forces loyal to the head of the region, whose mandate Mogadishu says expired four years ago.

The fighting broke out about six kilometres (3.7 miles) from the city of several hundred thousand inhabitants and local forces fled, Hassan Mohamed, a commander of the Somali National Army, told AFP.

"We have now entered the town from the side of the animal market, and very soon, we are planning to clear the rest of the city of the deposed regime loyalists," he told AFP.

"Their remnants are still in some parts of the town, but we will force them to retreat or surrender," he added.

Residents contacted by AFP confirmed that Somali army soldiers had entered the city, accompanied by fighters from a militia opposed to the local authorities.

"There was no fighting inside Baidoa so far, the opposition forces and the members of the national army have managed to enter the town after brief fighting in the suburbs of the town," Mahdi Ali, a resident, said by phone.

A few hours before pro-government forces entered Baidoa, an official from the South West State, where Baidoa is located, had insisted that local authorities and forces would repel any attack.

"Those who have invaded the people of the South West State will never succeed. They will be defeated," said Ugaas Hassan, spokesman for the state administration.

Deeply fractured Somalia's central government accuses the South West State president, Abdiaziz Hassan Mohamed Laftagareen, of having illegally extended his mandate, which in theory expired in 2022.

Tensions have risen recently after Laftagareen opposed a reform of the Somali constitution, adopted in early March, which extends the presidential term from four to five years and introduces the election of Somali MPs and senators by direct universal suffrage instead of the current indirect, clan-based system.

On Sunday, several security sources said Mogadishu had sent between 600 and 800 soldiers as reinforcements to retake Baidoa, supported by hundreds of local militiamen.

Laftagareen's fate and whereabouts are currently unknown.