Ticket sales at the Athens Olympics are set to top three million on Monday but stands are still barely half full as organisers struggle to fire up Greek sports fans.

However organisers firmly denied reports that they would be giving out free tickets to fill embarrassing gaps that show up so starkly in global television coverage.

After falling short on a promise to sell about 65 percent of the total 5.2 million tickets by the Games opening, organisers had hoped sales would rise as the Olympics became more exciting.

The 2000 Sydney Games, with almost double the total tickets available, were held mostly in front of capacity crowds.

Bombarded with questions at the daily briefing about ticket sales, Games spokesman Michael Zacharatos told reporters: "We are confident that today we will break the three million mark."

"Yesterday ticket sales versus net capacity was at 56 percent," he added. "We will not be giving out tickets and there will be no discounted tickets sold. That's a policy that is only fair to the people who have bought 2.9 million tickets so far."

He was at pains to point out that ticket sales at Barcelona in 1992 reached 3.21 million and just 2.7 million in Seoul in 1988.

Zacharatos refused to speculate on how sales from abroad might have been hit by the fear factor -- Greece has mounted Europe's biggest peacetime security operation at the first Summer Games since the September 11, 2001, attacks on the United States.

The International Olympic Committee, concerned the Games' image could be tarnished if competitions are held in front of half-empty stands, raised the issue with organisers on Sunday.

Crowds have been sparse in the badminton hall at the Goudi complex. Although the sport enjoys a huge following in much of Asia and pockets of Europe, Greece has no players of note and attendances have suffered.

Softball and baseball venues have been veritable wastelands. No one in Greece seems to want to sit in the blazing sun for two hours watching a sport they do not understand. Spectators at the swimming have been frying in the searing heat.

On Saturday only a sparse crowd saw Turkish weightlifter Nurcan Taylan claim her historic gold at the 5,000-seat Nikea weightlifting stadium, while former world number one Venus Williams won her first round match in front of only a handful of faithful fans in the new tennis arena.

The beach volleyball stadium with a capacity of about 10,000 was largely empty all day Saturday until the Greece match when it almost filled up.