MOGADISHU: Ethiopian and Somali troops captured a key Islamist militant stronghold in Somalia on Wednesday, as the rebels left their positions, a regional government official and residents said.

The loss of Baidoa in central Somalia is a major blow for the al Qaeda-backed al Shabaab rebel group which is also battling Kenyan troops to hold on to territory in southern Somalia and against African peacekeepers in pockets of the capital.

"We have taken Baidoa. There was no resistance from al Shabaab," said Abdifatah Mohamed Gesey, the governor of Somalia's Bay region.

Al Shabaab said its withdrawal from the city had been a tactical once aimed at avoiding casualties.

"Our fighters left town this morning without fighting. Now we are surrounding the town," said Sheikh Abdiasis Abu Musab, al Shabaab's spokesman for military operations.

"Baidoa will be a cemetery for the Ethiopians."

Earlier on Wednesday, a Baidoa resident who gave his name as Farah told Reuters no al Shabaab fighters were visible in the streets.

"Al Shabaab have run away to the Idaale jungle. Other residents tell me Ethiopian troops have reached the corners of the city," Farah told Reuters by telephone.

Ethiopia's forces launched a push south towards Baidoa through the neighbouring Bay and Bakool regions on Tuesday, making swift progress with the insurgents offering minimal resistance, said officials.

Located about 250 km north west of Mogadishu, Baidoa is considered the most important rebel base after the southern port city of Kismayu.

Baidoa hosted Somalia's interim government from early 2006, when another Islamist administration was battling warlords for control of Mogadishu, until the turn of 2008/2009 when al Shabaab seized the city and expelled the transitional government.

Ethiopia moved troops across the border into Somalia in November to open up a third front against the militants already suffering financial constraints after pulling most of their fighters out of Mogadishu and internal divisions.

On Wednesday morning, witnesses said al Shabaab had also surrendered the town of Berdale about 60 km for Baidoa.

Berdale resident Ali Mohamed Abukar said a "huge number" of heavily armed footsoldiers and columns of armoured vehicles and tanks had rolled into Berdale, a day after wresting control of the town of Yurkud about 50 km away.

"They were so many. They ordered as to remain calm and they headed towards Baidoa," Abukar told Reuters by telephone.