The Advertising Standards Authority has ruled that a US energy company misled the public when it made unsubstantiated claims about the benefits of fracking and claimed a gas shortage put the UK close to catastrophe.

Breitling Energy's advertisement in the Telegraph began: "Dear Citizens of the United Kingdom, do you know that your country is blessed with an incredible gift?" It said higher shale gas estimates in the British Geographical Survey were "fantastic news for the UK".

The ad, published in February, said Britain suffered a "near-catastrophic gas shortage" in early 2013 and claimed that extracting natural gas from shale rock would mean: "decades worth of natural gas", "millions of pounds in tax revenues", "freedom from interruptions and stoppages as a result of Russia's political games with your gas supply", "lowering energy prices for millions" and "reducing greenhouse emissions by replacing coal with natural gas for energy".

A reader complained to the ASA that the claims were misleading because they exaggerated the extent of Britain's gas shortage, the supposed benefits of fracking were not known, and Russia did not supply gas to the UK.

The ASA ruled against Breitling on all counts. It told the company it must not make its claims again and that future ads should be supported by hard evidence.

The government has backed fracking in the UK, to the consternation of environmental groups. The process, which involves drilling into the earth and using hydraulic pressure to extract previously unreachable gas, has been credited with bringing down US energy prices, but has proved divisive there as well.

Breitling produced press reports to back up its claim about gas supplies running short but it acknowledged that National Grid and the Department of Energy and Climate Change had said energy markets functioned normally at the time. Breitling cited David Cameron's assertion that fracking had "real potential" to cut energy bills but the ASA decided its claims about the virtues of fracking were misleading and exaggerated.

Breitling, based in Dallas, is one of the US energy industry's most vociferous advocates of fracking. Its chief executive, Chris Faulkner, has written a book called The Fracking Truth and produced a film, Breaking Free, promoting the benefits of the industry. A press release for Breaking Free says the US media refers to Faulkner as "The Frack Master".

Breitling said the ad was an open letter from Faulkner and that he was not trying to sell a product or service. "Our CEO simply was sharing his views and experience to bring some balance to the debate on hydraulic fracking in the UK, a debate which has been dominated for many months by the sometimes outrageous claims made by opponents of the fracking process.

"As our CEO sought to make known his views in the fracking debate, Breitling contends that the claims were properly phrased and that we had adequate substantiation for them."