The Federal Bureau of Investigation is leading an inquiry into the Twitter hacking, according to sources familiar with the situation, as more Washington lawmakers raised alarms about the breach of high-profile accounts on the social media platform.
Earlier, the law enforcement agency had said hackers appeared to commit cryptocurrency fraud after they seized control of the Twitter accounts of celebrities and political figures including Joe Biden, Kim Kardashian, Barack Obama and Elon Musk.
The FBI did not immediately respond to a question about it leading an inquiry into Twitter.
A day after the breach, it was not clear if the hackers were able to see private messages sent by the account holders. US lawmakers worried about future attacks.
"While this scheme appears financially motivated...imagine if these bad actors had a different intent to use powerful voices to spread disinformation to potentially interfere with our elections, disrupt the stock market, or upset our international relations," US Senator Ed Markey, a Democrat, said in a statement.
Twitter Inc said hackers had targeted employees with access to its internal systems and "used this access to take control of many highly-visible (including verified) accounts and Tweet on their behalf".
Other high-profile accounts that were hacked included rapper Kanye West, Amazon.com Inc founder Jeff Bezos, investor Warren Buffett, Microsoft Corp co-founder Bill Gates, and the corporate accounts for Uber Technologies Inc and Apple Inc.
Twitter's shares fell a little more than 1% on Thursday afternoon after paring earlier losses. In an extraordinary step, it temporarily prevented many verified accounts from publishing messages as it investigated the breach.
The hijacked accounts tweeted out messages telling users to send bitcoin and their money would be doubled. Publicly available blockchain records show that the apparent scammers received more than $100,000 worth of cryptocurrency.
CEO Jack Dorsey said in a tweet on Wednesday that it was a "tough day" for everyone at Twitter and pledged to share "everything we can when we have a more complete understanding of exactly what happened".