Facebook and Instagram have denied their services were hacked today, blaming a 40-minute outage on an internal systems issue.

The sites were unavailable across the world earlier today, with a hacking group appearing to claim responsibility for the outage.

A spokesman for Facebook, which owns Instagram, said: "Earlier today many people had trouble accessing Facebook and Instagram. This was not the result of a third party attack but instead occurred after we introduced a change that affected our configuration systems.

"We moved quickly to fix the problem, and both services are back to 100% for everyone."

The technical problems affected some other apps, including online dating service Tinder, which rely on Facebook servers to work.

A hacking group called Lizard Squad, which has previously claimed responsibility for bringing down online services, posted a message on Twitter this morning appearing to link itself to the outage.

It said: "Facebook, Instagram, Tinder, AIM, Hipchat #offline #LizardSquad".

Social media users, who were relieved to still be able to access Twitter, shared their complaints about the outage.

Scarlett Moffat, from the Channel 4 show Gogglebox, tweeted: "What Instagram and Facebook are down!! But how will I know what your morning Starbucks looks like."

Twitter user Vince Caso said: "Livetweeting is my last comfort. It is so difficult to judge people in 140 characters. I miss Facebook."

Fortune Feimster commented: "Facebook and Instagram are back up! Everyone can get out of their foetal position."