Taylor Swift on Friday lashed out at Ticketmaster over the botched sale of her upcoming tour, saying it was "excruciating" to learn that thousands of her fans had struggled to buy tickets.

The US pop mega-star's "The Eras Tour" was due to go on public sale Friday. But after days of glitches and long waits for those attempting to buy early pre-sale tickets, the public sale was abruptly canceled on Thursday.

"It's really difficult for me to trust an outside entity with these relationships and loyalties, and excruciating for me to just watch mistakes happen with no recourse," Swift wrote on Instagram.

Without naming Ticketmaster directly, Swift said she and her team had asked "them, multiple times, if they could handle this kind of demand and we were assured they could."

"It's truly amazing that 2.4 million people got tickets, but it really pisses me off that a lot of them feel like they went through several bear attacks to get them."

Ticketmaster, a dominating force in the ticketing industry, blamed "extraordinarily high demands on ticketing systems and insufficient remaining ticket inventory" for the public sale cancelation.

It cited a "staggering number of bot attacks" along with fans without pre-sale codes trying to purchase early tickets -- meaning their site experienced 3.5 billion system requests, they said, four times the company's previous peak.

It was not immediately clear whether the sale would be rescheduled, or how many unsold tickets remained. Ticketmaster did not respond to an AFP request for clarification.

Swift wrote Friday: "And to those who didn't get tickets, all I can say is that my hope is to provide more opportunities for us to all get together and sing these songs."

"The Eras Tour" marks Swift's first time back on the road since 2018's "Reputation" tour.

The multiple Grammy-winner has promised fans it will be "a journey through all of my musical eras of my career."

The tour is set to kick off March 17, 2023, in Glendale, Arizona, with stops including Houston, Atlanta, Chicago and five final domestic shows in Los Angeles in early August.

International shows will be announced at a later date.

- 'Unchecked monopoly' -

The American ticketing industry, which the company Ticketmaster overwhelmingly dominates, has for years left concertgoers frustrated by hidden fees, soaring costs, rampant scalpers and limited tickets due to presales.

The havoc over Swift's tour has spurred comment from a number of US lawmakers, including Alexandria Ocasio-Cortez and Richard Blumenthal, who urged an investigation into the "state of competition in the ticketing industry."

In 2010, Ticketmaster merged with event promotion behemoth Live Nation, creating what Congressman David Cicilline this week dubbed "an unchecked monopoly."

On Friday, the New York Times reported that the US Justice Department has opened an antitrust investigation into Ticketmaster's parent company.

The probe, focused on whether Live Nation Entertainment has abused its power over the live music industry, predates the botched sale of Swift's tour, two people with knowledge of the matter told the Times. The paper did not name them.

Neither the Justice Department nor Live Nation immediately responded to AFP requests for comment.

Live Nation recently has reported soaring demand after several pent-up pandemic years, saying ticket sales are up 37 percent compared to 2019.