Social networking website Twitter has confirmed that it has closed a "significant round of funding".

社交网站Twitter证实其接受了一个“重要的拨款”。

There are an estimated 45 million users of Twitter

Co-founder Evan Williams said in a blog post that the site had secured money from five investment firms.

However, he did not confirm earlier reports that suggested the firm had managed to secure $100 million (£62m), which would value the firm at $1bn.

The site, which allows users to write and share 140-character messages, has more than 45 million users worldwide.

The site had previously¹ raised $35m in February in a deal that valued the business then at $255m.

"It was important to us that we find investment partners who share our vision for building a company of enduring value," wrote Mr Williams.

"Twitter's journey has just begun."

Industry watchers have pointed² out that the firm still has no way of making money.

However, earlier this month the site revised its terms and conditions to allow advertising³ on its service.

"We leave the door open for advertising. We'd like to keep our options open," wrote co-founder Biz Stone in a blog.

The new funding has come from new investors⁴ Insight Venture Partners and T Rowe Price, as well as existing backers Institutional Venture Partners, Spark Capital and Benchmark Capital.