The organisers of the London Olympics say more tickets are to go on sale after the row over empty seats.
Locog said an initial 3000 tickets - including 600 for gymnastics - were "put back into the pot" and sold on the London 2012 website on Sunday night, the BBC reports.
More tickets returned by sports federations would be released the night before events, it added.
British Prime Minister David Cameron said the empty seats were "disappointing" but not "a unique episode", with other previous Games facing similar problems.
At some venues, seats in the accredited "Olympic family" areas - reserved for groups including officials, sports federations, athletes, journalists and sponsors - have remained empty.
Locog communications director Jackie Brock-Doyle said organisers were doing everything they could to fix the problem.