The bomb used to kill 22 people and injure dozens more used the same explosive as those used in the 7 July London bombings in 2005.
A US congressman has said the bomb used in the Manchester Arena attack was "a classic explosive device used by terrorists".
Texas Republican Mike McCaul, chairman of the House Homeland Security Committee, told The Associated Press the bomb used the explosive TATP.
The explosive, also known as Mother of Satan, was used in the deadly attacks in Paris in November 2015 and the March 2016 attack in Brussels, both carried out by Isis extremists.
Mr McCaul said the bomb suggests a "level of sophistication" that might indicate its maker had foreign training, and said the evidence gathered so far suggests "we're not dealing with a lone wolf situation."
Neighbours told Sky News they noticed the "strong smell of explosives" coming from under the door of the apartment used by the bomber, Salman Abedi.
The flat, located near Manchester Piccadilly station, is the last known location Abedi is known to have visited before leaving for Manchester Arena.
Security sources said the bomb he used was made using hydrogen peroxide, a component of TATP, and could have been manufactured "on a kitchen table".
A US official told NBC the "big and sophisticated" bomb was made with materials that are hard to obtain in Britain, meaning "it's almost impossible to see he didn't have help".
However, TATP is typically used by terror groups because it can be made using commonly available chemicals such as sulphuric acid, which is used to clean drains, hydrogen peroxide, which is used in hair dyes, and acetone.
It comes as police hunting the network behind Abedi said they had made "significant" arrests and officers had seized "very important" items in raids linked to the investigation.
Police and security services found bomb-making materials in the extensive raids following the attack, The Independent has learned.
One suspect device was detonated in a controlled explosion.
Several arrests have been made in both Britain and Libya after the bombing.
Eight men have been taken into custody in the UK, while the bomber's father and younger brother have been arrested in Libya, the latter of whom confessed to knowing "all the details" of the terror plot.
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