Twitter users worldwide were unable to access the service Tuesday morning because of technical issues affecting both web and mobile apps.

“Some users are currently experiencing problems accessing Twitter,” Twitter said in a message posted to Tumblr at about 4 a.m. ET. “We are aware of the issue and are working towards a resolution.”

The service’s technical problems began around 3:20 a.m. ET Tuesday, when Twitter users were met with error messages trying to access their timeline and tweets. Twitter service started to be restored about an hour later, but lingering problems continued throughout the morning.

As of 9 a.m. ET, Twitter’s timeline service had 85.3% uptime over the previous 24 hours, per the company’s status page for developers. UPDATE: As of 10:45 a.m. ET Twitter said all services were operating normally with only “performance issues” remaining for timelines.

While outages are disruptive for any Internet company, they’re particularly acute for Twitter, which positions the service’s real-time access to news and info as a core strength. Twitter shares fell as much as 3.5% Tuesday morning.

The outage comes as Twitter continues to struggle to grow its user base. For the third quarter of 2015, Twitter reported 307 million monthly active users on average, up only slightly from 304 million the prior quarter and an increase of 7% from the year-earlier base of 287 million monthly actives.

Last July, founder Jack Dorsey was reinstalled as Twitter’s CEO, replacing Dick Costolo, in a bid to boost the company’s performance and drive new product development as it lags social kingpin Facebook.