Azerbaijan has held a controversial referendum on constitutional amendments that are expected to strengthen the grip on power of President Ilham Aliyev and his family.

The Central Election Commission said turnout on September 26 was over 63 percent, surpassing the 25 percent required to validate the referendum.

Officials said referendum results will be announced by October 21.

The referendum includes 29 proposed amendments to the constitution.

Voters in the tightly controlled South Caucasus country didn't have to say "yes" or "no" to the whole package but instead could choose to approve or reject individual amendments.

The vote was monitored by observers from the Parliamentary Assembly of the Council of Europe (PACE) and the Commonwealth of Independent States (CIS).

Speaking in Baku on September 26, Russian Federation Council member Ilyas Umakhanov, head of the CIS monitoring mission, said the referendum was "very well prepared," adding that "former Soviet republics are exhibiting an innovative attitude and completely new norms of democratic development."

The most important of the proposed changes is an extension of the president's term of office from five to seven years.

If adopted, it would mean Aliyev, who has been in office since taking over from his ailing father in 2003, would not have to run again until 2020, instead of 2018.

The 54-year-old president would then only have to run again every seven years -- something he would be able to do repeatedly, since a presidential term limit was scrapped in 2009.

Another amendment seeks to create two vice-presidential posts, both of whose occupants would be appointed and dismissed by the president.

Presidential powers would devolve to the first vice president in the event that the president becomes incapable of discharging his duties -- rather than to the prime minister, who needs to be approved by parliament.

A further proposal empowers the president to schedule an early presidential election and dissolve parliament if twice in one year legislators pass no-confidence measures in the government or reject presidential nominees to key government posts.

The minimum age for presidential candidates, currently 35, would also be abolished and the age for election to the legislature lowered from 25 to 18.

Azerbaijan's ruling officials have defended the proposals contained in the referendum on stability and democracy grounds, while the opposition and other critics argue that it is intended to consolidate and prolong the grip on power by Aliyev and his family.

There has been speculation that the post of first vice president is being created for Aliyev's wife, Mehriban, who is a deputy chairwoman of the ruling New Azerbaijan Party, or for their 19-year-old son, Heidar.

In 2002 and 2009, Azerbaijan organized constitutional referendums marred by fraud that directly benefited the Aliyev family.

The Council of Europe's Venice Commission, which advises on constitutional issues, said on September 20 that many proposed constitutional changes would severely upset the balance of power and give “unprecedented” control to the president.

The commission also criticized the procedure of the referendum as having lacked proper debate in parliament and having been carried out too quickly and without real public discussion.

"We view that hasty conclusion [by the Venice Commission], which has many flaws, as politically driven,” Aliyev responded in a briefing in Baku on September 21. “They speak to us in a language of ultimatums."

Aliyev insisted that the proposed changes are designed to streamline the government and help introduce political and economic reforms.

Meanwhile, human rights groups have accused Azerbaijani authorities of unleashing a new wave of repression to silence critical voices ahead of the referendum, with a number of activists being harassed, detained, arrested, and/or fined.

The oil-rich South Caucasus nation has faced growing social and economic problems stemming from falling world oil prices in recent years.

With reporting by APA and Trend