Operating losses at Klarna, a "buy now, pay later" company, widened to 3.13 billion crowns ($344.1 million) in the January-September period, from 801 million crowns a year ago.
Net credit losses rose by over 80% to 2.9 billion crowns, Klarna, which rivals Affirm and Afterpay, said.
In the third quarter, the firm's gross merchandise volume (GMV) - the value of transactions made using its payment platform - grew to over $57 billion in the third quarter from $35 billion.
"The US continues to be Klarna's fastest growing market with over 300% GMV growth YTD driven by 21m+ consumers," the firm, which is expected to make its stock market debut in the coming months, said in a statement.
The firm's investors include SoftBank, Sequoia Capital, NorthZone, Silver Lake, rapper Snoop Dogg, BlackRock and Singapore's sovereign wealth fund GIC.
($1 = 9.0963 Swedish crowns)
(Reporting by Helena Soderpalm; Editing by Simon Johnson)