Several people are reported to have been killed in southern Somalia as violence erupted following the arrest of a former al-Shabab commander set to contest regional elections.
At least 11 people, including soldiers and civilians, died in Baidoa during clashes involving supporters of Mukhtar Robow, sources told the BBC.
The government has accused Mr Robow of being a security threat.
He is seeking the presidency of South West state in next week's election.
News of Mr Robow's arrest early on Thursday triggered street protests in Baidoa, the regional capital.
A Somali radio station tweeted images of roads strewn with burning tyres and rocks.
Photos : Casualties reported as Southwest administrative headquarters Baidoa is hit by violent protests as supporters of detained leading southwest presidential candidate and former Alshabaab deputy Mukhtar Robow clash with security agents #Somalia pic.twitter.com/YT3t7IzFab— Radio Dalsan (@DalsanFM) December 13, 2018
Among those killed in protests was a member of the regional parliament, Baidoa elder Saleh Isak told Reuters news agency.
An African Union peacekeeping force (Amisom) is in Somalia to help the government fight al-Shabab, an Islamist militant group.
On Friday afternoon, Baidoa residents described the city as calm but tense, with shops closed and most residents staying indoors.
"Amisom's armoured vehicles came into the town as a patrol," said one resident, Halima Mohamed.
"They went back after they saw it was calm and that some residents blocked some of the roads with big stones."
The BBC's Ibrahim Adan in the capital, Mogadishu, says the nationality of the soldiers who were killed is not clear. Ethiopian troops, who form part of the Amisom force, have a base in the city.
Robow a threat to government control
Analysis by Tomi Oladipo, BBC Africa security correspondent
Mukhtar Robow's defection last year from al-Shabab was much-touted by Somalia's UN backed-government as a success in its fight against the militants. The 49-year-old trained in Afghanistan and was a founder member of the al-Qaeda-linked group. But his standing with the government collapsed when he announced his candidacy to become president of South West state.
This poses a threat to the government's intended control of the area through its preferred candidate, Abdiaziz Lafta Gareen.
But in Somalia clan politics is powerful - and Mr Robow belongs to the Leysan sub-clan, one of the largest in the state. The government's campaign against him has actually brought him more attention and boosted his popularity.
The arrest has backfired as it seems the powerbrokers in the capital, Mogadishu, did not predict these protests in Baidoa. The situation is likely to deteriorate if his candidacy in next week's elections is cancelled, as the government tried to do when it initially banned him from contesting in October.
Ethiopia and the African Union mission in Somalia have remained silent about the alleged involvement of Ethiopian troops in the arrest. They would need a good reason to have been involved, otherwise they will only gain enemies in Somalia who see them as partisan and meddling in local politics.
Mr Robow was a spokesman for al-Shabab and once served as its deputy leader before defecting last year.
Two months ago, the federal government banned him from contesting the state elections but the electoral commission gave him the go-ahead.
Following his arrest, a government statement said he had been organising a militia in Baidoa.
"These actions indicate that he never relinquished his extremist ideologies and is ready to harm the Somali people again," the statement said.
Mr Robow is supported by several clans in the area and is regarded as a serious candidate. His supporters were infuriated by his detention.
"This is a violation of democracy, Robow was standing in his region and his people wanted him. The government has no right to arrest him," Baidoa resident Mohamed Sheik Ali told AFP news agency.