The United States is denouncing "violence, intimidation, and harassment" in Burundi against people thought to oppose a referendum this month that would allow the president to stay in power for another 14 years.The State Department statement expressed concern about the "non-transparent process" of changing the constitution in the May 17 referendum. It says incumbents' efforts to stay in office beyond term limits weaken democratic institutions.The East African nation has seen political violence since President Pierre Nkurunziza sought a disputed third term in 2015. An estimated 1 200 people have been killed. More than 400 000 people have fled the country.The referendum's proposal could extend the president's term from five years to seven, meaning Nkurunziza could rule for another 14 years when his current term expires in 2020.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.