Parts of Twitter became inaccessible a day before thousands of fans are expected to start tweeting about the Olympic Games.
The Twitter.com site was unreachable for almost an hour, and continued to suffer intermittent faults thereafter.
The service was still accessible via its mobile site and other applications.
In a message to users, the company said: "Howdy folks, looks like we're experiencing a small interruption of Twitter.com and some mobile clients."
On its network status page, the company wrote: "Our engineers are currently working to resolve the issue."
It is not yet known what caused the fault. Users that could access the service reported that shortened URL links included in tweets were not working properly.
Twitter is expected to be one of the main social networks to be used by both fans and athletes during the Games.
Reliability and stability
Sporting events regularly attract the service's biggest audience.
During Spain's Euro 2012 win, there were over 15,000 tweets every second.
For London 2012, there are over 2,000 verified Olympians - past and present - that are signed up to use the service.
Downtime plagued Twitter during its early years, but subsequent investment meant the site has become more reliable.
Last month, Twitter blamed a "cascading bug" for causing "turbulence" on the service which made the site slow or inaccessible for about two hours.
At the time, Mazen Rawashdeh, the site's vice president of engineering, apologised to users but praised the site's recent reliability record.
"For the past six months, we've enjoyed our highest marks for site reliability and stability ever: at least 99.96% and often 99.99%.
"In simpler terms, this means that in an average 24-hour period, twitter.com has been stable and available to everyone for roughly 23 hours, 59 minutes and 40-ish seconds."
Source BBC News