Facebook and Instagram were down temporarily late Monday, suggesting that common infrastructure used by these services was hit. Facebook later said the problems were its fault.
"We're aware of an outage affecting Instagram and are working on a fix. Thank you for your patience," Instagram said in a Twitter message, which was deleted after the service was restored.
Users in various parts of the world were reporting that Facebook was down. People accessing Facebook's website received a message: "Sorry, something went wrong. We're working on it and we'll get it fixed as soon as we can."
Some users were reporting that some other websites were also down. HipChat, one of the services named, said it had a database issue but some systems were back online, while the Tinder app reported that its service was back.
The outages come as a "life-threatening blizzard" hit the North East of the U.S., putting at risk a variety of operations including online services.
Users later reported that both Facebook and Instagram were back.
A Facebook spokeswoman wrote in an email, after the services were back, that many people had trouble earlier in the evening accessing Facebook and Instagram after it introduced "a change that affected our configuration systems."
The access problems were "not the result of a third party attack," she wrote, in an apparent reference to some news reports that a hacker group, the Lizard Squad, had hinted that it may have been responsible. On Monday, the group claimed responsibility for an attack on the website of Malaysia Airlines.