Gmail, YouTube and other services that rely on Google’s technology were disrupted for several hours on Sunday by what the company said were “high levels of network congestion.”

It was not clear what specifically was behind the network problems, which Google said it first began investigating around 4 p.m. Eastern time.

Google did not say how it believes the problems originated. The issues appeared to affect more than a dozen Google services, including its cloud computing technology, which is used by many companies to power their own services and apps.

Google said the problems were not caused by a cyberattack, as hypothesized by some on social media. As of 7 p.m., Google said the issue was “resolved for all users.”