STOCKHOLM, Aug 25 (Reuters) - Swedish payments firm Klarna said on Wednesday it would continue to enter new markets, as it reported a jump in transactions using its platform in the second quarter. The "buy now, pay later" company, which is expected to make its stock market debut in the coming months, said the number of users in the United States grew by 3 million to 20 million. Klarna, which is currently active in 17 countries, said it saw growth in all its key markets and would keep up expansion. "With a proven concept for market expansion, Klarna will continue to grow by entering new markets and continuing to diversify revenue streams," it said in a statement. Along with rivals such as Affirm and Afterpay (APT.AX), Klarna has seen a surge in demand as the coronavirus pandemic has driven a shift in consumer spending online. The company did not give details on its widely expected stock market listing, though many bankers predict it will list in New York in early 2022. Klarna, which allows shoppers to buy online through its merchant partners and settle their dues in instalments, raised $639 million in June from a group of investors, lifting its valuation to about $46 billion. read more The firm"s gross merchandise volume - the value of transactions made using its payment platform - grew to over $20 billion in the three months ending June 30 from $12 billion a year ago. Its operating loss widened to 1.76 billion crowns ($202.6 million) in the January-June period, from 690 million crowns. Klarna is among the largest players in the global payments sector, with over 90 million global active users. It processes 2 million transactions a day. Its investors include SoftBank (9984.T), Sequoia Capital, NorthZone, Silver Lake, rapper Snoop Dogg, BlackRock (BLK.N) and Singapore"s sovereign wealth fund GIC. ($1 = 8.6878 Swedish crowns)