ZAMBIAN police said they arrested 151 people following riots in parts of the country’s Southern province after Edgar Lungu was re-elected as president on August 11.

The main opposition party said the vote was stolen and that it would challenge its validity in the constitutional court.

Protests broke out in at least five towns in Southern province, where opposition leader Hakainde Hichilema won most of the votes, Godwin Phiri, police commissioner for the province, said in comments broadcast by state television.

Rioters burnt at least four shops and two houses in places including the provincial capital, he said.

The situation has since been brought under control and patrols have been intensified in the province, police spokesman Rae Hamoonga said in an e-mailed statement.

Supporters of the opposition United Party for National Development were “going around targeting ruling Patriotic Front members,” Phiri said. “They are going to answer to the law.”

Lungu won the elections with 50.4% of the vote, while Hichilema got 47.6%. The opposition leader, who has unsuccessfully run for the presidency on four previous occasions, said he would not accept the result, as the electoral commission had colluded with the ruling party to steal the elections, which they both denied.

A dispute could delay plans to secure a bailout package from the International Monetary Fund, according to Robert Besseling, director at Johannesburg-based risk consultancy Exx Africa.

Hichilema called on his supporters to be “active”, when he said he would reject the election outcome on August 13.

“We will fight for Zambians but we invite you to be part of this process,” he said. “This docility will damage your children and your great-grandchildren in years to come.”