Image copyright Getty Images Image caption AirBnB is the second most valuable start-up company in the US

Home rental company AirBnB has raised $1bn (£821m) of investment funding in a deal that values the firm at $31bn.

The San Francisco-based firm disclosed the investment in a filing to the US Securities and Exchange Commission.

AirBnB did not comment on how it would use the funding, but is expected to expand its operations globally.

It has grown rapidly since its launch in 2008, and currently operates in 65,000 cities worldwide.

The firm, which does not publish its sales figures, makes its money by enabling homeowners to rent out their homes.

It takes a 3% cut of each booking and a 6% to 12% service charge from guests.

'No IPO plans'

It made its first profit in the second half of 2016, and will continue to be profitable this year on an underlying basis, according to media stories.

They also reported that the firm had no plans to list its shares on the stock market in the near future.

Image copyright Getty Images Image caption Brian Chesky co-founded AirBnB in 2008 to help pay the rent on his San Francisco flat

AirBnB has been diversifying and recently began offering users new services, such as tailor-made city tours and exclusive experiences with local experts.

However, it has also faced criticism over claims it is driving up rents and contributing to housing shortages in some cities.

In December, under pressure from MPs, the firm said it would block hosts in London from renting out homes for more than 90 days a year without official consent.

It is also facing tougher regulations in New York, Berlin and Barcelona.

What is AirBnB?

The accommodation site lets people rent out their properties, often at prices undercutting hotels and traditional Bed and Breakfasts.

It was started by university friends Brian Chesky and Joe Gebbia in 2008 to help pay the rent on their San Francisco flat.

As the site expanded into more and more cities, helped by the use of professional photographers, it attracted backers including Amazon founder Jeff Bezos and actor Ashton Kutcher.

In total it has raised more than $3bn from investors and it is now the second most valuable start-up in the US after Uber, which is valued at about $70bn.