The U.S. ambassador to Azerbaijan, Ann Derse, has said she hopes Baku will investigate allegations of police interference against opposition activists.
Azerbaijani opposition activists say they have faced intimidation and arrest when collecting signatures opposing a referendum that would remove presidential term limits from the constitution.
Derse told RFE/RL's Azerbaijani Service that "society has to take part in the free and fair process" of any changes to the constitution.
Opposition activist Azer Nagiyev said that he was accused of forcing people to sign a petition against the referendum and that police made him testify against himself.
Others, including those who have signed the petition, have reported being harassed by police. An Interior Ministry spokesman told RFE/RL that police are acting legally, and are pursuing opposition activists who have broken the law by deceiving people into signing the petitions.