Thousands of Microsoft Outlook users reported issues accessing their email accounts on Monday morning.

More than 15,000 users reported issues with Microsoft 365, the web version of the Microsoft Outlook application, according to outage-tracking site DownDetector. Reports of the outage began to tick up at around 10 am ET, according to DownDetector data.

"We're investigating an issue with accessing Outlook on the web," the company tweeted from its Microsoft 365 Status support handle.

In a follow-up tweet, the company added, "We're reviewing our networking systems and recent updates in an effort to identify the underlying root cause of the issue."

The Twitter thread continued to say that the company has "identified downstream impact" for other Microsoft tools, including Teams, SharePoint Online and OneDrive for Business.

Microsoft did not immediately respond to CNN's request for comment Monday morning.

This is a developing story. Please check back for updates.