LONDON — Social media services Facebook, WhatsApp and Instagram have been hit by an outage lasting more than an hour. All three services are owned by Facebook and could not be accessed over the web or smartphone apps.

Down Detector, which tracks outages, logged nearly 80,000 reports for WhatsApp and more than 50,000 for Facebook. Data from the website suggests the outage is affecting user accounts across the world.

Some people also reported problems using Facebook's virtual reality headset platform, Oculus.

Facebook said: "We are aware some people are having trouble accessing our apps and products. We are working to get things back to normal as quickly as possible and apologize for any inconvenience."

No official reason for the problem was given. Online network experts speculated it may involve an error with DNS, or the domain name system, for Facebook sites.

DNS is often compared to an address book or phone book for the internet, pointing web browsers to the computer system which serves the website they are looking for.

Previous issues with DNS led to widespread outages of several major sites earlier this year.

In one of those instances, it emerged that the blackout was caused by a single customer of a widely-used service who changed their settings, triggering a software bug affecting a huge number of websites.

It is rare for such problems to affect a single tech giant such as Facebook, or for the issue to remain unfixed for a long time.

The outage came the morning after "60 Minutes" aired a segment in which Facebook whistleblower Frances Haugen claimed the company is aware of how its platforms are used to spread hate, violence and misinformation, and that Facebook has tried to hide that evidence. Facebook has pushed back on those claims.

The interview followed weeks of reporting about and criticism of Facebook after Haugen released thousands of pages of internal documents to regulators and the Wall Street Journal. Haugen is set to testify before a Senate subcommittee on Tuesday.

Shares of Facebook were down more than 5% in midday trading Monday, putting it on pace for its worst trading day in nearly a year. — Agencies