The constitution requires that President Joseph Kabila, in power since 2001, step down after the polls, but opponents accuse him of delaying the vote to hold onto power.
Congolese authorities have refused to renew the visa of a prominent American human rights activist, the government said on Tuesday, a decision that follows expulsions of other foreign researchers in a tense election year.
Government spokesman Lambert Mende did not say why the visa of Ida Sawyer, U.S.-based Human Rights Watch's senior researcher in Democratic Republic of Congo, was not renewed or when she would need to leave the country.
Sawyer, who has worked for Human Rights Watch in Congo since 2008, has been among the most vocal critics of what the United Nations and rights groups say is a growing crackdown on dissent before elections scheduled for November.
In a statement, Human Rights Watch Executive Director Kenneth Roth called the move "a brazen attempt to muzzle reporting on the government's brutal repression of those supporting presidential term limits".
The constitution requires that President Joseph Kabila, in power since 2001, step down after the polls, but opponents accuse him of delaying the vote to hold onto power. The government says that enrolling new voters will take more than a year.
Dozens of people were killed in anti-government protests in January 2015 over a proposed revision to the country's electoral code that could have delayed the election by years.
Sawyer criticised security forces at the time of using "unlawful and excessive force". In January this year, she called for targeted sanctions against officials responsible for violence against civilians.
The government denies using excessive force against protesters or targeting its political opponents.
The U.S. government imposed sanctions on the capital Kinshasa's police chief in June for what it described as the violent suppression of opposition to Kabila's government.
The Congolese government in April expelled Jason Stearns, the American director of New York University's Congo Research Group, shortly after he published a report linking soldiers to massacres of civilians.
Two Global Witness activists investigating logging practices were also forced to leave last month, accused of inciting a local community to revolt. The London-based NGO denied the allegations.