Police in Zambia freed an opposition leader on Thursday after holding him in detention for a week on accusations of defaming President Edgar Lungu, an offence that carries a maximum five-year prison term.

Police arrested United Progressive Party leader Saviour Chishimba last Thursday and said he would be charged with defaming the president.

“We have discontinued the case,” police spokeswoman Esther Mwaata-Katongo said in a statement, without giving any reasons.

Chishimba hit the headlines in July after criticising Lungu’s decision to impose emergency powers and suggesting the president should go to hospital for mental tests.

Political tensions in Zambia, once seen as one of Africa’s more stable and functional democracies, have been rising since main opposition leader Hakainde Hichilema was arrested on treason charges in April.