Using the hashtag #LondonAttacks, ISIS fighters have announced their plans for a bombing campaign in the capital.
The sick boasts include pictures of a cache of machine guns piled into the back of a car with the words: "Bismallah [in the name of God] we are coming".
Another user tweeted "just learnt how to make suicide belt by my brother…will be using in #LondonAttack" alongside a photo of what appears to be a crudely-made package wrapped in duct-tape.
The messages come amid ongoing concerns about the rise of ISIS-affiliated groups operating in the West.
Just last week, two men launched an attack on an exhibition containing drawings of the Prophet Muhammed in Texas.
A manual circulated online also shares tips for "how to survive in the West", including options would-be terrorists have for smuggling weapons in cars and evading the security services.
The latest warnings of an attack in London saw some Twitter users give details of the specific location of an alleged strike, with one user claiming Floral Street in Covent Garden was the intended target.
The Metropolitan Police are investigating the threats but are downplaying the likelihood of anyone carrying out an attack.
Paddington tube station was also picked out as a possible target, with the comment: “Let the reality hit home, the taste of chaos, carnage & bloodshed. #foreignpolicy #QaribanQariba.”
Another message posted on Twitter said: "Brothers n Sisters if you are in Europe stay away from police stations or government buildings".
A number of accounts linked with the terror posts were later suspended by Twitter.
A spokesperson for the Met said: "We are aware of message circulating on social media and are investigating.
"There is nothing at this time to suggest it is a credible threat."
It comes as members of the brutal terror regime threatened to launch a cyber-war on senior European and US leaders.
In a video released yesterday, the group claimed to have hacked websites linked to the “American leadership”.
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A group calling itself the “Islamic State’s Defenders in the Internet” reportedly released the three-and-a-half-minute video, which warned that “the electronic war has not yet begun”.
“We observe all the movements that you are doing from your devices,” the video said.
“Soon you will see how we control your electronic world.
