Azerbaijani officials say voters have overwhelmingly approved constitutional amendments scrapping presidential term limits, in a vote the opposition boycotted.
Azerbaijan's Central Elections Commission reported a 71 percent turnout for Wednesday's ballot. It said about 92 percent of those voting approved an end to term limits. Critics say this will effectively clear the way for President Ilham Aliyev to extend his rule indefinitely.
A Council of Europe delegation praised the conduct of the vote, but urged further political reforms.
Opposition Musavat party leader Isa Gambar said party observers monitored "thousands of violations."
In Washington, a State Department spokeswoman expressed U.S. concern over the speed with which the referendum was put forward and restrictions on media and assembly which limited public debate. She also noted reports of interference by police and officials during the campaign and on the day of the vote.
The spokeswoman said the United Sates continues to call on the Azerbaijan's government to fully respect fundamental freedoms, including those of expression, association and assembly. She also urged Azerbaijani authorities to fully investigate reports of interference in the referendum process
The president's critics have accused the United States and Europe of ignoring recent political and media restrictions imposed by the Aliyev government, for fear of losing access to the country's vast energy reserves.
President Aliyev won a second five-year term in October. He came to power in 2003 after succeeding his father, Heydar Aliyev, who dominated the country in various posts for more than 30 years.
Some information for this report was provided by AFP, AP and Reuters.