The bureau has responded after a number of high-profile US figures - including the likes of Bill Gates, Joe Biden and Elon Musk - were hit in the attack as their official accounts requested donations in the cryptocurrency.
In a statement, the FBI said "the accounts appear to have been compromised" with the goal of cryptocurrency fraud, as they urged the public to remain vigilant.
As reported by the BBC, the US Senate Commerce committee has told Twitter to brief it on the issue by July 23.
In a series of posts on the Twitter Support account, the social networking site said their investigation "is still ongoing" but updated its users on the situation.
They said: "We detected what we believe to be a coordinated social engineering attack by people who successfully targeted some of our employees with access to internal systems and tools.
"We know they used this access to take control of many highly-visible (including verified) accounts and Tweet on their behalf.
"We're looking into what other malicious activity they may have conducted or information they may have accessed and will share more here as we have it."
The company noted they removed tweets posted by the attackers, and "limited functionality for a much larger group of accounts", which included all verified pages.
They later added: "Based on what we know right now, we believe approximately 130 accounts were targeted by the attackers in some way as part of the incident.
"For a small subset of these accounts, the attackers were able to gain control of the accounts and then send Tweets from those accounts.
"We're working with impacted account owners and will continue to do so over the next several days.
"We are continuing to assess whether non-public data related to these accounts was compromised, and will provide updates if we determine that occurred."