ANKARA (Reuters) - Turkish prosecutors said on Thursday they were investigating allegations that President Tayyip Erdogan s family moved millions of dollars abroad to avoid taxes, saying there were doubts about the authenticity of documents behind the claims. The chairman of the main opposition Republican People s Party (CHP), Kemal Kilicdaroglu, accused members of Erdogan s family earlier this week of transferring $14 million to a company in the Isle of Man, holding up documents he said proved the transactions had taken place. [nL8N1NZ43I] Erdogan dismissed the allegations as lies and said on Thursday Kilicdaroglu would  pay the price . Erdogan has dominated Turkish politics for almost 15 years and remains by far the country s most popular leader. Opponents accuse him of increasingly authoritarian conduct, especially since a failed military coup last year; but the CHP struggles to rally support in challenging the President. The CHP has not accused Erdogan or his family members or any companies it says were involved in transactions of any criminal activity. The Ankara prosecutor s office said it was launching an investigation into the allegations and that an official from the company which Kilicdaroglu named as the destination of Erdogan family funds, Bellway LTD, had called the documents fake.  It also asked the CHP to hand over all documents. Ozgur Ozel, deputy chairman of the CHP, said the party would comply with the request from prosecutors.  The CHP has also filed a parliamentary motion requesting an investigation into its allegations, but the assembly, dominated by Erdogan s ruling AK party, rejected the motion on Thursday. 