ISTANBUL - Turkish President Recep Tayyip Erdogan warned on Sunday that the country's embattled bid to join the European Union will be back "on the table" after next week's referendum on enhancing his powers, raising new doubts about the future of the membership drive.

In a speech in the Aegean city of Izmir, Erdogan described Europe as a "sick man", using the jibe that nineteenth century European politicians used to describe the decaying Ottoman Empire.

"Europe will pay for what they have done. God willing, the question of the European Union will again be on the table after April 16," Erdogan said.

He said that Turks living in Europe were "oppressed" and "humiliated": "God willing, our people will bring them (Europe) to account," he said.

"They said a century ago that we were the 'sick man'. Now they are the 'sick man'. Europe is collapsing," he added, claiming the European economy weakened every year.

The EU is facing the gravest crisis in its six-decade history after last year's British vote to leave the bloc, while euroskeptic movements have gained ground across the continent.

Erdogan reaffirmed that if a bill on restoring the death penalty - abolished in 2004 as part of the EU bid - was brought to him he would sign it "without hesitation".

The president has raised hackles over recent weeks by claiming some EU states were behaving like the Nazis by preventing his ministers from holding pre-election rallies.

While the 'No' campaign has struggled to make its voice heard as the 'Yes' campaign dominates the airwaves, analysts believe the outcome is still too close to call as the race enters the last week of campaigning.

Sunday marked the last day of expatriate voting in the referendum which is expected to be crucial to the outcome with some three million expatriate voters registered, almost half of them in Germany.

The 'Yes' campaign is also backed by the Nationalist Movement Party which on Sunday held a giant rally led by its leader Devlet Bahceli in Istanbul at precisely the same shoreside venue used by Erdogan for a giant meeting the day earlier.