Only six of the 12 World Cup stadiums will offer free wi-fi so fans can connect to the Internet from the bleachers, official sources said Tuesday.

According to the union of Brazilian telecom firms (Sinditelebrasil), wi-fi service won't be ready in time at the stadiums in Sao Paulo, Belo Horizonte, Fortaleza, Recife, Curitiba and Natal.

Brazilian officials wanted to turn all the stadiums into wi-fi hotspots to avoid overloading the 2G, 3G or 4G services during the games, but succeeded in equipping only the venues in Brasilia, Porto Alegre, Salvador, Rio de Janeiro, Manaus and Cuiaba.

Sinditelebrasil's executive president, Eduardo Levy, blamed the lack of coverage on the difficult negotiations between the telecoms and the stadium managers.

"What we didn't do, is not because we didn't want to, it was because we couldn't, we didn't have access," Levy said.

To provide Internet coverage at all 12 venues during the World Cup, the firms installed 3,724 cellphone antennas throughout the stadiums offering 2G, 3G and 4G service, using the same technology installed at the 2012 London Olympic Games.

The installed capacity allows up to 300,000 simultaneous calls per hour, with an average duration of 2.4 minutes each, as well as 24,000 simultaneous data connections per hour, so a 0.55 MB image can be sent in 2.5 seconds.