Burundi's constitutional court has upheld the results of the May 17 referendum showing most voters supported constitutional changes that could allow the president to stay in power until 2034.

The court on Thursday rejected a petition filed by the opposition alleging intimidation and abuse, validating the official results showing more than 73 percent of 4.7 million voters supported the amendments.

The changes include extending the president's term from five years to seven. That could give President Pierre Nkurunziza, in power since 2005, another 14 years when his current term expires in 2020.

The East African nation has seen sporadic but deadly political violence since April 2015, when Nkurunziza sought a disputed third term.

More than 1,200 people have been killed since then, according to the United Nations.