Twitter has rebuffed suggestions that it is about to start charging companies to use its micro-blogging service.

The source of the speculation was an interview with Twitter co-founder Biz Stone, which appeared on the Marketing magazine web site early on 10 February.

In the article, Stone is quoted as saying: "We are noticing more companies using Twitter and individuals following them. We can identify ways to make this experience even more valuable and charge for commercial accounts."

Based on Stone's comments, there was a flurry of reports on the web that Twitter was about to start charging firms already using the service to continue with their accounts.

However, Stone was quick to play down this speculation in a blog entry posted on the Twitter site last night.

In the post, titled 'Nothing to report just yet', Stone noted that Twitter had been "thinking out loud" for over a year about the use of the service by commercial organisations, and how the offering could be improved.

"We hope to begin iterating on revenue products this year," Stone said. " However, it's important to note that, whatever we come up with, Twitter will remain free to use by everyone - individuals, companies, celebrities, etc. What we're thinking about is adding value in places where we are already seeing traction, not imposing fees on existing services."

He added that there was no official announcement at present as the plans were still at a very early stage.