London (CNN) -- London 2012 organizers are asking sports federations to return any surplus tickets so they can be onsold, following a public outcry over empty seats at Olympic venues.
While thousands of fans have missed out on tickets, seats in the accredited "Olympic family" areas -- reserved for groups including officials, sports federations, athletes, journalists and sponsors -- have remained empty at some venues.
A spokeswoman for the organizing committee said about 3,000 tickets had been recovered and sold Sunday via the official London 2012 website.
"We talked to the International Federations yesterday, we were able to put back into the pot for sale around 3,000 tickets last night. They have all been sold," Jackie Brock-Doyle, the organizing committee's director of communications, told reporters Monday.
"We're doing this session by session, talking to the accredited groups, including obviously broadcast media and everybody else, and asking whether we can release, for the different sessions, tickets back into the public pot."
Politicians and sporting associations have also reacted angrily to the empty seats.
Colin Moynihan, chairman of the British Olympic Association, said full venues were important for athletes and fans, and suggested implementing a "30-minute rule" whereby seats would be forfeited if left vacant. His suggestion was later backed by British Culture Secretary Jeremy Hunt.
Athletes have also expressed dismay that their families have been unable to attend events.
Irish swimmer Barry Murphy tweeted: "Hundreds of empty seats again in the Aquatic Center. My parents would've given an arm and leg to get in."
Indian tennis player Mahesh Bhupathi tweeted: "Been trying for 6 hours now to buy my wife a ticket to watch me play tomorrow. Still no luck, and the grounds here feel empty. Absurd!!!"
The organizing committee said Sunday it was addressing the issue partly by offering empty seats in accredited areas to soldiers who had finished their security shifts, but remained on the grounds.
"If they want to sit there and watch, they can," said Sebastian Coe, chairman of the organizing committee. "It's not mobilizing the army to solve this."
Organizers plan to place members of the public in the unused "accredited seats," which typically have some of the best views of the action, through a variety of approaches, said the organizing committee's head of media Joanna Manning-Cooper.
Some seats are being filled with students and teachers from London schools, who were already on the Olympic Park, while others are being given as "upgrades" to members of the public in poorer seats.
Organizers have also implemented a Wimbledon-style scheme to recycle tickets at hockey, basketball, handball and water polo double-bills, where some fans have been leaving after watching their team. On the first day of competition, about 300 handball tickets were re-sold to people already at the Olympic Park.
Coe insisted the venues were "stuffed" with fans, and suggested empty seats were to be expected in the early stages of the competition "as people are figuring out how and where they're going to spend their time."
"Let's not run away with ourselves here," he told reporters. "This is a moveable situation, it will resolve itself quite quickly."
He said it was not unusual for members of official delegations to have heavy commitments.
"My day yesterday is a good example -- I went to about four venues and only stayed for about an hour in each one."
The empty seats have provoked a range of responses from dismay to anger on social media. Twitter user @stevegtennis posted a picture of a block of empty seats at Wimbledon with the message: "Sorry to report there are loads of empty seats at the #Olympics tennis. Outrage. Please RT (re-tweet) in protest."
Another user, @marksregard, complained: "All those empty seats...and I know folks that tried for months to get tickets and were unsuccessful."
Reports that Olympic sponsors were to blame for the empty seats prompted a number of official sponsors, including GE, Visa, P&G and Coca Cola to issue statements that they were using their allocations responsibly.
But organizers said the sponsors were not to blame for leaving seats empty.
British Culture Secretary Jeremy Hunt told the BBC Monday that although the seats were not being used, organizers did not have the right to demand that sports federations returned the tickets.
"What we're saying to the IOC and to the international sports federations is if you're not going to use them, could we have as many possible back because of course we've got lots of members of the public who would dearly love to go?"
"We want to be completely upfront with the public -- this is a negotiation, we don't have a right to demand these back."