The Central Asian republic's Azat (Freedom) Social Democratic Party at a party congress unanimously voted for co-chairman Bulat Abilov, the independent Interfax-Kazakhstan news agency reported.

Nazarbyaev earlier issued a decree to conduct the April 3 polls after unexpectedly rejecting a plan to hold a referendum on whether he could serve as president until 2020 without elections.

The Kazakh opposition party last week called for the oil-rich country to hold its "first fair and transparent" elections and announced it would field a candidate.

The current parliament is made up entirely of Nazarbayev supporters and critics have complained that opposition activists are silenced by what is seen as an increasingly authoritarian regime.

A new five-year term at the helm of the Central Asian former Soviet republic would extend 70 year-old leader's rule to a third decade.

Along with Uzbek President Islam Karimov, who rose to power at the same time, Nazarbayev is the longest-serving leader in the former Soviet states.

Election campaigning is to start on March 3 and end on April