Polls have closed in Azerbaijan, where voters cast ballots in a controversial referendum abolishing presidential term limits in the oil-rich country.

More than 60 percent of eligible voters cast their ballots on 29 constitutional amendments, one of which would abolish Azerbaijan's presidential term limits. 

Opposition groups have called the referendum a step back from democracy and urged citizens to boycott the vote. A turnout of 25 percent is needed for the results to be valid.

President Ilham Aliyev won a second five-year term in October.  He first came to power in 2003 after succeeding his father, Heydar Aliyev, who dominated the country in various posts for more than 30 years.

Earlier this week, the Council of Europe asked Azerbaijan to postpone the vote.

The acting president of the group's congress, Ian Micallef, warned that if the referendum passes, Azerbaijan would find itself in a very difficult situation with a constitution that does not conform to European democratic standards.

Opponents have warned that passage of the referendum would give President Aliyev the ability to remain in office for life.  They also 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.

Some information for this report was provided by AFP and Reuters