A group of hackers is threatening to take the gaming networks related to Xbox and PlayStation consoles offline for a week during Christmas, mirroring a similar attack last year that stopped gamers around the world from accessing games.

The group, which calls itself Phantom Squad, says it has already started attacking various gaming networks, including PlayStation Network (PSN), Xbox Live and Grand Theft Auto 5, and on Tuesday morning it said it had taken Reddit offline with a cyberattack. Reddit was offline for a period early Tuesday morning, but it is unclear at this stage what or who was responsible, as Phantom Squad's tweet claiming credit for the attack came after the first reports of problems from people accessing Reddit.

International Business Times has contacted Reddit to ask if it went offline as a result of a cyberattack, but at the time of publication there has been no response. According to the Reddit Status website, the problem was due to some of its databases coming "under extreme load," which could have been caused by a distributed denial of service (DDoS) attack -- the tool Phantom Squad is promising to use against PSN and Xbox Live servers at Christmas.

The threat to take the networks offline for a week was first made on Dec. 9:

We are going to shut down Xbox live and PSN this year on christmas. And we are going to keep them down for one week straight #DramaAlert — Phantom Squad (@PhantomSqaud) December 9, 2015

Last year, a group of hackers known as Lizard Squad attacked Xbox Live and PSN on Christmas Day, rendering the services inaccessible for gamers around the world. Three members of Lizard Squad were subsequently arrested and charged with various offenses related to their hacking activities. The attacks only stopped when internet entrepreneur and well-known gamer Kim Dotcom promised to give Lizard Squad 3,000 accounts on his encrypted upload service Mega.

Dotcom has once again involved himself in the potential attacks this year, warning Sony and Microsoft that they have had one year to upgrade their systems following the Lizard Squad attacks last year, adding that he doubts he will be able to stop them again:

Warning @Sony & @Microsoft. You had 1 year to upgrade your networks. If Lizard Squad takes down PSN & XBOX this Xmas, we'll be pissed! RT! — Kim Dotcom (@KimDotcom) December 14, 2015

Phantom Squad has made a reference to Lizard Squad on Twitter, and said Tuesday that if one of its tweets was retweeted 100 times, it would "declare war on Lizard Squad," but so far the message has received only 41 retweets.

Besides claiming to have taken Reddit offline briefly, the group also claims to have attacked servers running GTA 5 and Black Ops 3, as well as taking Xbox Live and PSN offline for brief spells. The group published a video as proof of the attacks, showing tweets claiming responsibility for the attacks alongside images from the website Down Detector, which monitors online outages for a variety of services online.

Phantom Squad says that the group is made up of just five members and the reason it carries out the attacks is "because cybersecurity does not exist." IBT has contacted both Sony and Microsoft to assess if the companies are aware of the threats made against their respective networks, but there was no response by the time of publication.