Some of the fake news segments talked up success in the war in Iraq, or promoted the companies' products.

Investigators from the Federal Communications Commission are seeking information about stations across the country after a report by a campaign group detailed the extraordinary extent of the use of such items. The report, by the non-profit Centre for Media And Democracy, found that over a 10-month period at least 77 television stations used the false news broadcasts, known as Video News Releases (VNRs).

Not one told viewers who had produced the items.

"We know we only had partial access to these VNRs and yet we found 77 stations using them, " said Diana Farsetta, one of the researchers. "I would say it's pretty extraordinary. The picture we found was much worse than we expected going into the investigation in terms of just how widely these get played and how frequently these pre-packaged segments are put on the air."

Farsetta said the public relations companies commissioned to produce these segments by corporations had become increasingly sophisticated in their techniques in order to get the VNRs broadcast. "They have got very good at mimicking what a real, independently-produced television news report would look like, " she said.

The FCC has declined to comment on the investigation but investigators from the commission's enforcement unit recently approached Farsetta for a copy of her group's report.

Among items provided by the Bush administration to news stations was one in which an IraqiAmerican in Kansas City was seen saying "Thank you Bush. Thank you USA" in response to the 2003 fall of Baghdad. The footage was actually produced by the state department, one of 20 federal agencies that have produced and distributed such items.

Many of the corporate reports, produced by drugs manufacturers such as Pfizer, focus on health issues and promote the manufacturer's products. One example cited by the report was a Hallowe'en segment produced by confectionery giant Mars, which featured Snickers, M&Ms and other brands. While the original VNR disclosed that it was produced by Mars, that information was removed when it was broadcast by a Fox-owned station in St Louis.

Bloomberg news service said other companies that sponsored the promotions included General Motors, the world's largest car maker, and Intel, the biggest maker of semiconductors. All of the companies said they included full disclosure of their involvement.

"We in no way attempt to hide that we are providing the video, " said Chuck Mulloy, a spokesman for Intel. "In fact, we bend over backward to make this disclosure."

The FCC was urged to act by a lobbying campaign organised by Free Press, another non-profit group that focuses on media policy. Spokesman Craig Aaron said more than 25,000 people had written to the FCC about VNRs.

"Essentially it's corporate advertising or propaganda masquerading as news, " he said. "The public obviously expects their news reports are going to be based on real reporting and real information. If they are watching an advertisement for a company or a government policy, they need to be told."

Last spring the FCC warned broadcasters that they were obliged to inform viewers if items were sponsored. The maximum fine for each violation is $32,500.