GENEVA (AP) — An independent human rights expert working with the United Nations is calling on Myanmar’s government and military leadership to stop persecuting supporters of the opposition ahead of Sunday’s general election.

Thomas Andrews, a former U.S. congressman from Maine who is the U.N. special investigator on Myanmar, called for free and fair elections but expressed concerns about the denial of the vote to Rohingya Muslims and others based on race, ethnicity or religion.

Andrews, who as an independent “special rapporteur” does not speak for the U.N., said the Myanmar army is using a penal code set up under colonialist Britain in 1861 to “lock up journalists, students and others for exercising their basic right to free expression.”

He also lamented allegations of state censorship of some candidates.

Myanmar’s electoral commission has canceled voting in several parts of the country facing bouts of unrest.

Michelle Bachelet, who heads the office of the U.N. High Commissioner for Human Rights, has also expressed serious concerns about the human rights situation in Myanmar before the vote, including violations of the right to political participation, particularly for minority groups.

The last general election in 2015 brought to power Aung San Suu Kyi and her National League for Democracy after more than five decades of military rule. Suu Kyi, a Nobel Peace Prize laureate, and her government have faced international condemnation for allowing security forces to carry out widespread abuses of the Rohingya minority, driving more than 700,000 to seek safety in neighboring Bangladesh.