Taylor Swift says it was "excruciating" to watch fans struggle to buy tickets for her upcoming US tour, after sales descended into chaos this week.

Ticketmaster was criticised over its handling of the sales - which saw widespread site crashes in the presale and then cancellation of the main sale.

But responding on Instagram, US pop star Swift said she had been assured that Ticketmaster could handle demand.

"We asked them, multiple times, if they could handle this kind of demand and we were assured they could," she wrote, in her first public statement addressing the fiasco.

Swift said it was "truly amazing that 2.4 million people got tickets" but annoyed her that "a lot of them feel like they went through several bear attacks to get them".

Many fans in the presale complained the website crashed repeatedly after waiting hours in the queue. She added she was "trying to figure out how this situation can be improved moving forward".

On Friday evening, Ticketmaster issued a statement to apologise and explain what went wrong. Ticketmaster is already subject to government monitoring

Swift's US tour will kick off in March next year in Arizona. She has not yet announced an international tour.