By Avril Ormsby and Paul Sandle
LONDON (Reuters) - Sports fans attending the London Olympics were told on Sunday to avoid non-urgent text messages and tweets during events because overloading of data networks was affecting television coverage.
Commentators on Saturday's men's cycling road race were unable to tell viewers how far the leaders were ahead of the chasing pack because data could not get through from the GPS satellite navigation system travelling with the cyclists.
It was particularly annoying for British viewers, who had tuned in hoping to see a medal for sprint king Mark Cavendish.
Many inadvertently made matters worse by venting their anger on Twitter at the lack of information.
An International Olympic Committee spokesman said the network problem had been caused by the messages sent by the hundreds of thousands of fans who lined the streets to cheer on the British team.
"Of course, if you want to send something, we are not going to say 'Don't, you can't do it', and we would certainly never prevent people," he said. "It's just - if it's not an urgent, urgent one, please kind of take it easy."
Other events due to take place on London's roads include the men's and women's marathon and triathlon.
An explosion in the use of mobile phones to access the Internet and take and send photos and video has made London 2012 the first true "social media Games", but also put pressure on the networks. The host broadcaster, the BBC, is enabling fans to see many events live on their smartphones.
Mobile operators and infrastructure companies had said they expected to be able to meet the extra demand.
The IOC spokesman said it appeared the problem lay with oversubscription on one particular network, and talks had taken place in an attempt to share more of the data. "It's a network issue, and it is that which we are working on," he said.
Official 2012 Olympic communications services provider BT, Vodafone and O2, owned by Spain's Telefonica, said they had not seen any network problems.
BT says it has provided four times the network capacity of the 2008 Beijing Games to meet the increased demand, laying enough cable to stretch between London and New York.
O2, subcontracted by BT to provide mobile services within the Olympic Village, suffered a glitch this month when a third of its customers were hit by a 24-hour network failure.
Steven Hartley at Ovum Telecoms Strategy said at the time that, while mobile capacity was being upgraded at transport and crowd hotspots, spikes in demand at peripheral sites could prove disastrous.
Television coverage is in the hands of the Olympic Broadcasting Services, created by the IOC to ensure uniform coverage at all Games.
The IOC spokesman conceded that asking people not to send messages at key moments "may not have an awful lot of effect".
(This version of the story makes it clear that BT, not Vodafone, is official Olympic provider in paragraph 11)
(Editing by Kevin Liffey)