Prosper - like rival outfits Lending Club and Loanio - was forced to close its doors to new loans last year as it looked to register its business with the Securities and Exchange Commission.

But last month it received an intra-state exemption from the California Department of Corporations. This meant Californian residents and businesses could make loans, with anyone in the US able to borrow.

However, SEC registration was not completed and the company has now "decided to voluntarily shut down" operations until this is done.

Says the firm: "As a result, due to regulatory concerns, and in the interest of working toward getting our registration statement effective as soon as possible, we are discontinuing our California intrastate offering at this time."

Existing lenders and borrowers will be unaffected.

The company has provided no explanation for the quick U-turn or guidance on when it expects to start business again, saying only this will be "in the hopefully not too distant future".