WAAGACUSUB.COM - Somalia has released without charge a former minister and critic of the government who spent two days in jail after being arrested for alleged treason, a lawmaker said on Thursday.

The arrest of Abdirahman Abdishakur, who was a candidate in a February election won by President Mohamed Abdullahi Mohamed, followed mounting pressure on the president and his UN-backed government to end an Islamist insurgency.

"Last night at midnight, they released ex-minister Abdirahman Abdishakur,” lawmaker Mahad Salad told Reuters.

The MP said he, other colleagues and the ex-minister were going to court on Thursday to "know the evidence on what he (Abdishakur) was first arrested”.

Islamist militants al Shabaab have been stepping up pressure on Mohamed’s government by staging frequent and increasingly large-scale bombings against both civilian and military targets in recent months in the capital Mogadishu and elsewhere.

The group is fighting to expel African Union peacekeeping force AMISOM from Somalia, topple the federal government and impose rule based on its strict interpretation of Islam’s sharia law.

More than 500 people were killed in twin bomb blasts in Mogadishu in October while this month a suicide bomber killed at least 18 people at a Mogadishu police academy.

At a news conference after his arrest, Somalian attorney general Ahmed Ali Dahir had described Abdishakur’s house as a hub for the opposition and a gathering point for people who wanted to replace the government.

Early on Thursday, al Shabaab militants ambushed three vehicles belonging to the military’s U.S.-trained special forces unit Danab on a road between Mogadishu and the town of Wanlaweyn.

The group said it seized the three cars while residents said they saw two burning cars.

Police Major Ahmed Nur told Reuters al Shabaab had targeted the convoy with a roadside bomb before ambushing it.

"We sent reinforcement to the area but we believe many died from both sides,” he said.

"We ambushed the so-called military commandos and took their pickups,” Abdiasis Abu Musab, al Shabaab’s military operation spokesman, said.

Somalia has been locked in lawlessness and violence since the early 1990s, following the ouster of dictator Mohamed Siad Barre.