Prime Minister Erdoğan expressed multiple times that Turkey would acknowledge the mass killings of up to 1.5 million Armenians during World War I as genocide only after a thorough investigation by a joint Turkish-Armenian commission consisting of historians, archaeologists, political scientists and other experts. In 2005, Erdoğan and the main opposition party leader Deniz Baykal wrote a letter to Armenian President Robert Kocharian, proposing the creation of a joint Turkish-Armenian commission. Armenian Foreign Minister Vartan Oskanian rejected the offer because he asserted that the proposal itself was "insincere and not serious". He added: "This issue cannot be considered at historical level with Turks, who themselves politicized the problem".