Erdogan said Turkey had negotiated an extension “with the support of our Russian friends and the efforts of our Ukrainian friends”.
Kiev confirmed an extension of the agreement in a statement later on Wednesday.
Moscow also agreed to an extension, but expressed dissatisfaction with what it called “differences”.
Western observers believe that Russia is trying to delay exports by slowing inspections of ships’ cargoes, and that Moscow is demanding sanctions relief in the negotiations.
According to the agreement, all exports must be checked so that only grain is loaded.
The UN is also a party to the negotiations on grain exports.
The agreement was brokered at the initiative of the UN and Turkey at the end of July last year. The settlement has been extended in the past, but the most recent agreement was set to expire on Thursday.