A court in Burundi has jailed an official who allegedly called for the drowning of the government's opponents.

The charging and conviction of Melchiade Nzopfabarushe in just hours is rare punishment for a government supporter in this country plagued by the threat of violence stemming from the president's political moves.

Tensions are rising over the May 17 referendum proposing a constitutional change that would allow President Pierre Nkurunziza to extend his rule.

Nzopfabrushe, who once worked in Nkurunziza's office, is a senior official with the governing party in Bujumbura's Kabezi neighborhood.

iBurundi, a group of activists monitoring the government's alleged crimes, dismissed his conviction as a "side show."

In a video circulating on Twitter, Nzopfabarushe is seen saying those opposed to the referendum will be thrown into Lake Tanganyika.