Amnesty International has called on Republic of Congo authorities to unconditionally release an opposition leader detained for more than two months.

The organization said Monday that Paulin Makaya was detained and charged for exercising his right to freedom of expression by participating in an October protest against amendments to the constitution in Brazzaville.

Amnesty International says Makaya and others arrested are prisoners of conscience. It says all charges should be dropped in the run-up to national elections.

Republic of Congo opposition leaders called for a boycott of an Oct. 25 referendum vote that ultimately passed to allow the country's longtime president to seek another term.

Amnesty says 16 people died in clashes during demonstrations in Brazzaville and Pointe Noire.

Elections originally scheduled for July, will be held March 20.