Turkey opposition accuses Erdogan family of offshore financial transfers
Republican People's Party (CHP) chief Kemal Kilicdaroglu alleged that members of the president's family, including his brother, transferred around $15 million to Bellway Limited, based in the low-tax British Crown Dependency of the Isle of Man.
"We have all the records of this company. Was money sent to this company? Yes it was sent," Kilicdaroglu told CHP party members in Ankara.
He then listed the alleged transfers made by family members including Erdogan's son, Ahmet Burak Erdogan, between 2011 and 2012 to the company.
Other CHP members at one point chanted "Tayyip, resign!" during the speech.
"You say to citizens, 'give taxes otherwise I will give a three-fold penalty' but you will have another established for your children, loved ones and send millions of dollars from Turkey!" Kilicdaroglu said.
Erdogan at the weekend promised that he would "not stay one minute more as president" if Kilicdaroglu could prove his claims.
Calling on Erdogan to resign in light of his accusations, Kilicdaroglu said: "If you are an honourable man, you will do what is necessary."
It was not possible to immediately verify the CHP leader's accusations.
Erdogan's lawyer Ahmet Ozel was quoted by state-run news agency Anadolu as saying that the documents Kilicdaroglu presented were "fake".
AKP MP Bulent Turan dismissed the claims as "foolish and unfounded" and said all the accusations were "lies".
Turan also urged Kilicdaroglu to resign, arguing he had not proved his claims.
Erdogan has yet to react to the claims but in speeches during the past week he has repeatedly railed against the CHP leader and his party.
When Kilicdaroglu previously demanded to know whether Erdogan was aware that his family were "sending millions of dollars of money to tax havens", the president responded by suing him for hundreds of thousands of dollars last week.
A similar investigation was launched in 2016 against Kilicdaroglu after he repeatedly called Erdogan a "tinpot dictator".
Thousands of Turks have been prosecuted in recent years, including cartoonists, a former Miss Turkey winner and schoolchildren, on accusations of insulting Erdogan but most of the complaints did not lead to jail time.
Following the failed July 15 coup last year, Erdogan said he would drop outstanding cases in a one-off gesture.