A salesman hands tickets to a sports fan after he bought them at the 2016 Rio Olympics ticket office in Rio de Janeiro Brazil, June 20, 2016. REUTERS/Ricardo Moraes/File Photo

RIO DE JANEIRO (Reuters) - Two days ahead of the opening ceremony at the Olympics, organizers say that 1.3 million tickets remained unsold, an indication that spectator demand for Rio has lagged behind previous summer Games.

As of Friday, 4.8 million tickets for the Games had been sold, out of around 6.1 million tickets on offer, the Rio Organising Committee told Reuters on Wednesday. Demand has been strong for sports such as basketball and swimming, the committee said.

Some 500,000 of the unsold tickets are for soccer matches. Many of those matches are scheduled to be played in stadiums in other Brazilian cities far from Rio.

Tickets for the Rio Games have been available since early 2015, but factors including a sluggish Brazilian economy and concerns about the presence of Zika virus in Brazil may have had an impact on both domestic and international demand.

A month before the London Games in 2012, 7 million tickets had already been sold, or more than 80 percent. Ultimately, more than 8 million were sold there.

Ahead of the Beijing Games in 2008, some 6.8 million tickets were put on sale and more than 95 percent were sold, according to an Olympic Committee report.

Rio organizers had initially planned to sell up to 7.5 million event tickets, but later pared back their estimate to closer to 6 million, citing factors including space limitations at event venues.

Ticket sales are an important generator of revenue for a city where around $12 billion has been spent preparing for the Games. Remaining tickets are still available to fans through the committee’s website, Rio2016.com.