NAIROBI (Reuters) - An official of Burundi’s ruling party was sentenced to three years in jail on Monday for urging government supporters to throw opponents into a lake ahead of a May 17 referendum on extending President Pierre Nkurunziza’s term in office.

Authorities in Burundi arrested Melchiade Nzopfabarushe after he made the comments on Sunday at a party rally in his native village.

Nzopfabarushe was summarily convicted of making a “verbal threat against the population, inciting people to revolt against the administration and the spreading of rumors” in a rare punishment for a ruling party official.

His lawyer told reporters his client would appeal against the judgment.

The incident came amid increased political jitters in Burundi, whose modern history has been marred by ethnically-charged civil war.

The Justice Ministry spokesman did not immediately reply to a request for comment.

Nearly 430,000 people, including opposition politicians, have fled the East African nation of 10.5 million people since Nkurunziza won a third term in a 2015 election that led to violent clashes. His foes said he had no right to run again.

“We said that we have ordered boats. We will send them (opponents) into Lake Tanganyika,” Nzopfabarushe said in a video clip of his comments, which have been circulating online, to the party members in Kabezi, near the capital Bujumbura.

“He who has the president’s support successfully achieves his endeavors. That is the message we are giving either here or nationwide,” said Nzopfabarushe, a former senior official in the president’s office.

The ruling CNDD FDD party sought to dissociate itself from Nzopfabarushe’s comments, saying on Twitter it rejected “any subversive message which may jeopardize unity and cohesion among the Burundian people”.

The party also said it had asked the justice ministry to investigate all cases of divisive language used by politicians ahead of the May vote.

The referendum would extend the presidential term to seven years from five, allowing Nkurunziza to run again in 2020. It would limit the president to two consecutive seven-year terms, but would not take into account previous terms, potentially extending his rule to 2034.

Human rights groups say they doubt the vote will take place in a free and fair climate.

Nkurunziza came to power in 2005 after a peace deal ended a decade of civil war between the Tutsi-dominated army and Hutu rebels, in which 300,000 people were killed.

He ran for a third term in 2015, which opponents said violated the terms of the peace deal, sparking clashes that resulted in hundreds of deaths.