Turkish President Recep Tayyip Erdogan was set Tuesday to rejoin the ruling party after an absence of almost three years, the first major change to come into effect following the referendum victory on boosting his powers.

Erdogan last month narrowly won a referendum on a new constitution creating a presidential system with just over 51 percent of the vote.

Under the old system, the head of state had to sever ties with their political party. Erdogan had to leave the ruling Justice and Development Party (AKP) when he became president in August 2014 after more than a decade as premier. 

But a key change is that the president can be a member of a political party, allowing Erdogan to return to the AKP which he co-founded in 2001 as a new Islamic-rooted force in Turkish politics and which has dominated the scene ever since.

Erdogan will be welcomed as a new member at a ceremony at party headquarters in Ankara and he is then expected to give a speech, according to AKP spokesman Yasin Aktay.

Aktay said Erdogan will also likely be reinstalled as party chairman on May 21 at an extraordinary AKP congress.

"During this congress, there will be an election and we envisage that the president will be elected as party chairman," Aktay told reporters.

As AKP head, Erdogan will replace Prime Minister Binali Yildirim who is set to stay on as premier.

The new constitution envisages sweeping changes including the abolition of the premier's post and giving the head of state power to appoint ministers.

But these changes will only come into force after November 2019 elections and the party membership shift is one of the few measures to take effect before then.

Erdogan co-founded the AKP along with other conservative heavyweights, including his predecessor Abdullah Gul who has yet to return to the party following his 2007-2014 presidency.

There was speculation in the Turkish media about whether Gul would attend the ceremony but Aktay said special invitations had not been made.

Supporters of the new system say it will bring Turkey efficient governance but opponents fear it will set the country on the path to authoritarian rule.