So far only Italian capital Rome has been officially confirmed as a candidate with the deadline for announcing bids being September 1.
"Istanbul will bid," IOC Executive Board member Richard Carrion told Reuters on the sidelines of the IOC session.
Among the other cities reported to be close to bidding is Madrid, who lost in the final round of voting to Rio de Janeiro for the 2016 Games and possibly Japan's capital Tokyo.
South Africa's Durban could also lodge a bid despite the government's initial decision to quash the idea and instead invest the money into improving services for South Africans.
The country's sports minister Fikile Mbalula has said all doors were open with IOC officials also hinting there could be a government u-turn on Durban.
A decision on the 2020 host will be taken in 2013.