Elon Musk's ownership of Twitter descended deeper into chaos as key security executives resigned from the platform, drawing a sharp warning from US regulators.

The walkouts came after a turbulent launch of new Twitter features following the Tesla and SpaceX owner's $44 billion buyout of the influential messaging app.

Musk warned employees Thursday that the site was burning through cash dangerously fast, raising the specter of bankruptcy if the situation was not turned around.

"I've made the hard decision to leave Twitter," tweeted chief security officer Lea Kissner, who reportedly stepped down with other key privacy or security executives.

In the most extraordinary exit, US media reported that Yoel Roth -- the site's head of trust and safety -- stepped down just a day after staunchly defending Musk's content moderation policy to advertisers.

Late on Thursday, Roth's Twitter bio identified him as "Former Head of Trust & Safety at @Twitter."

Media reports had said Robin Wheeler, who held a key role linking Twitter with advertisers and was considered a key Musk ally inside the company, was leaving but late Thursday she tweeted: "I'm still here."

The site's update included a launch of the long-awaited Twitter Blue subscription service, which allowed users to pay $7.99 per month for a coveted blue tick, as well as a separate gray "official" badge for some high-profile accounts.

But on Wednesday Musk scrapped the new gray label almost immediately, overshadowing the launch of the paid service, which is only available on the mobile app on iPhones and in the United States.

The launch also saw the emergence of a flurry of fake accounts as users used the opportunity to impersonate celebrities and politicians such as NBA star LeBron James or former British prime minister Tony Blair.

'Deep concern'

The chaos drew a rare warning from the Federal Trade Commission, the US authority overseeing consumer safety that had put Twitter under watch for past security and privacy breaches.

"We are tracking recent developments at Twitter with deep concern," an FTC spokesperson said in a statement.

"No CEO or company is above the law, and companies must follow our consent decrees," the spokesperson added, referring to past commitments by Twitter to obey US privacy rules.

Violating FTC decisions could cost Twitter millions of dollars in fines.

Musk fired half of the 7,500 employees of the California company a week ago, 10 days after buying the site and becoming its sole owner.

For the first time since the layoffs, the 51-year-old entrepreneur on Thursday addressed his remaining employees and urged them to help the site reach one billion users, according to employee text messages seen by AFP.

Musk also warned that the company was bleeding cash and expressed fear about the effects of the poor economy on his newly bought business.

"You may have noticed I sold a bunch of Tesla stock. The reason I did that is to save Twitter," he is reported to have said.

Wedbush analyst Dan Ives warned that the Twitter episode could have serious repercussions for electric car manufacturer Tesla.

"Brand destruction is our biggest worry with this Twitter circus show. It's that simple and I can't ignore it for Tesla stock," Ives wrote on the site.

Twitter is also crippled by the decision of advertisers to stay away from the platform, concerned about Musk's plans.

The tycoon announced he was ending work-from-home policies at Twitter, which had been a widespread practice at the San Francisco-based company.

"If you don't show up at the office, resignation accepted," he told employees.

© Agence France-Presse