The United States on Tuesday dealt a blow to U.S. manufacturers of solar panels and boosted shares in their Chinese rivals when it imposed preliminary punitive duties of less than 5 percent on imports from China.

The Coalition for American Solar Manufacturing, a U.S. industry group that has complained that massive Chinese subsidies were driving them out of business, put the best face on the lower-than-expected initial duties.

It said it believed the U.S. Commerce Department would uncover more subsidies and unfair pricing practices as it continues its probe in the coming months, which would result in higher final duties.

Today's announcement affirms what U.S. manufacturers have long known: Chinese manufacturers have received unfair and WTO-illegal subsidies, said Steve Ostrenga, chief executive officer of Helios Solar Works in Milwaukee, Wisconsin.

We appreciate the Commerce Department's hard work in bringing these subsidies to light, and we look forward to addressing all of China's unfair trade practices in the solar industry.

The United States imported $2.8 billion worth of solar cells and panels from China in 2011, up sharply from about $1.2 billion in 2010, according to industry estimates.

The Commerce Department will announce preliminary anti-dumping duties in May to address a separate set of charges that Chinese producers are selling solar panels in the U.S. market at unfairly low prices.

Chinese producers and U.S. companies opposed to the duties said the preliminary decision belied charges the Chinese government was flooding the Chinese solar sector with subsidies.

We're pleased and in large part feel vindicated, Robert Petrina, managing director of Yingli Green Energy's U.S. business said. I think it is a positive outcome and I think it really speaks to the crux of the argument that Chinese producers are not heavily subsidized.

The Commerce Department determined Chinese solar cell and panel manufacturers received government subsidies worth 2.90 percent to 4.73 percent of the value of their product, industry officials on both sides of the case said.

Importers will have to post bonds or cash deposits based on the preliminary countervailing duty rates while the department continues its investigation.

SolarWorld Industries America, the U.S. arm of leading German solar manufacturer SolarWorld AG, has led the U.S. industry coalition seeking import relief.

The group says U.S. production of solar cells and panels is threatened by Chinese competitors that receive generous government subsidies and dump their products in the United States at unfairly low prices.

Analysts had expected preliminary countervailing duties in the range of 20 percent to 30 percent.

Instead, the Commerce Department set a preliminary duty of 2.90 percent on SunTech Power Holdings, the world's biggest producer of photovoltaic solar panels, and a preliminary duty of 4.73 percent on Trina Solar, another major Chinese producer, industry officials said. All other Chinese solar panel producers and exporters received a duty rate of 3.59 percent.

Shares in SunTech, which had fallen earlier in the day, quickly jumped after the report to trade 16 percent higher, while Trina Solar shares rallied 10 percent and Yingli Green Energy shares surged 14 percent.

(Reporting By Doug Palmer and Matt Daily in New York; Editing by Anthony Boadle and Eric Walsh)

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