Kemal Kilicdaroglu of the Republican People’s Party (CHP) has repeatedly criticised Erdogan’s profligacy in campaign speeches ahead of a June 7 parliamentary election.

“Gentlemen in Ankara, palaces have been built for you, planes bought, Mercedes cars purchased … golden seats have been bought, that’s how you use the toilet,” Kilicdaroglu said at a rally in the Aegean city of Izmir on Saturday.

Erdogan, who moved into the controversial new 1,000-room palace complex after winning a presidential election last August, challenged Kilicdaroglu to prove his assertion.

“I invite him to please come and take a tour … I wonder if he will be able to find such a golden toilet seat in any of these washrooms,” Erdogan said in an interview with state broadcaster TRT late on Sunday.

“If he finds it, I will resign from the presidency.”

Brightly illuminated at night and sitting on a hilltop, the complex – nicknamed Ak Saray or the White Palace – dominates the skyline on the western edge of the Turkish capital.

Previous heads of state used a more modest old palace, but Erdogan’s move came as he launched what he has dubbed a “New Turkey“, in which he aspires to amend the constitution and create a full executive presidential system.

Erdogan wants the ruling AK Party, which he founded more than a decade ago, to win a strong enough majority on June 7 to change the constitution unopposed, but opinion polls suggest it will struggle to do so.