Facebook and Instagram were down temporarily late Monday, suggesting that common infrastructure used by these services was hit.
"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."
Facebook could not be immediately reached for comment. Some users were reporting that some other websites were also down but it could not be immediately confirmed.
The outages come as a "life-threatening blizzard" hit the North East of the U.S., but it wasn't clear whether it had affected the online services.
Users later reported that both Facebook and Instagram were back, though neither website explained what had caused the outage.