MOGADISHU (Reuters) - Somalia arrested on Thursday a former Islamist militant who seeking election as a regional president, sparking clashes between his supporters and security forces.

FILE PHOTO: Former al Shabaab leader Mukhtar Robow attends a news conference in Baidoa, Somalia, November 4, 2018. REUTERS/Feisal Omar/File Photo

The arrest of Mukhtar Robow in an area where al Shabaab militants retain a presence after a long civil war heightened tension between Somalia’s central government and semi-autonomous regions where elections are scheduled over the coming months.

The Internal Security Ministry in Mogadishu said its forces had arrested Robow on the suspicion that he had brought militants and weapons back to the southern city of Baidoa, the capital of South West region where he is running for president.

The ministry asked Robow to denounce “his ideology of terrorism...and support the federal government of Somalia”.

Robow, a former prominent al Shabaab insurgent and group spokesman, publicly renounced violence and recognized federal authority in August 2017.

Earlier on Thursday, Robow’s spokesman said he was also beaten by Ethiopian troops, who are part of an African Union peacekeeping force in Somalia, in the course of his arrest.

A spokesman for Ethiopia’s foreign ministry said he had no information on any Ethiopian involvement in Robow’s arrest.

Baidoa residents said the arrest sparked off clashes between Baidoa militiamen loyal to Robow and Somali and Ethiopian security forces.

“There are casualties. We see Ethiopian tanks being moved into the town. Now there is sporadic gunfire. Tension is very high now and all shops are closed,” Ahmed Abdullahi, a Baidoa shopkeeper, told Reuters.

Analysts said Robow’s detention would only heighten his standing in South West. “A thoroughly daft move on part of the Ethiopians. They have now made him a martyr, increased his popularity even more,” Rashid Abdi, Horn of Africa Project Director at International Crisis Group, said on Twitter.

The U.S.-backed Mogadishu government tried to bar Robow’s presidential candidacy in South West, citing remaining U.S. sanctions against him. But the state electoral commission last month dismissed Mogadishu’s demands and accepted his candidacy.

South West will be the first of Somalia’s seven semi-autonomous regions to hold presidential elections in the coming months, a critical juncture in a growing power struggle between the U.S.-backed central government and regions where militants retain a presence following a long civil war.

However, on Dec. 1 the commission postponed South West’s vote for the third time, saying it was not sufficiently prepared amid lingering tensions with Mogadishu.

Somalia has been trying to claw its way out of the embers of the civil war that engulfed it in 1991, when clan warlords overthrew a dictator and then turned on each other.

Al Shabaab has sought for over a decade to topple the central government and implement its strict version of Islamic law. It was driven out of the capital in 2011 but maintains a foothold in some regions including South West.