It's not clear how widespread the outages were in the United States. By mid-morning on the East Coast, desktop and mobile versions of Twitter appeared to be working, though the company wouldn't say if they were back to normal. A company spokeswoman also wouldn't reveal any details as to the possible cause of the outage.
Twitter, which has 320 million active users, tweeted that it was aware of the issue and was trying to fix it.
Users said the service was not accessible on desktop computers. There were complaints of users receiving a "server error" just before 8 a.m. Eastern. Twitter's mobile app was partially functioning for some users but its timeline updated new tweets sporadically. Its search function appeared disabled as some hashtags or keyword searches returned no results.
Twitter has suffered several service disruptions so far this year. On Monday, some users could not access Twitter on mobile and web for about 10 minutes. The service was disrupted on Friday for about 20 minutes.