China's latest crackdown on intellectual property piracy has netted more than 20,000 fake Tibetan-language text books, 90,000 copies of a well-known Chinese film as well as porn films, state media said on Friday.

The United States and other Western countries have repeatedly complained that China has not kept promises to stamp out intellectual property theft.

Countless pledges from Beijing to get tough have also failed to stamp out the problem, and pirated goods are commonly found in shops and on the streets of the Chinese capital.

In the latest effort to convince a skeptical world its efforts are paying off, the official Xinhua news agency said Chinese courts had given sentences of up to six years in jail to 18 people for pirating the text books and films.

"In one case, Zhang Xinfeng was found to sell more than 30,000 copies of textbooks, including more than 20,000 Tibetan books, to 25 schools in 19 Tibetan cities and counties between September 2009 to September 2010," the report said.

Zhang got five years in jail and a 100,000 yuan ($15,521) fine, Xinhua said.

Two other people were also given jail time for producing 90,000 copies of the 2010 Chinese film, "Let the Bullets Fly," by award-winning director Jiang Wen, as well as "porn discs," it added without elaborating.

Xinhua said the sentences were "the latest move to show the country's determination to combat piracy."

U.S. Department of Commerce General Counsel Cameron Kerry, in Beijing this week on a visit focused on anti-corruption and commercial rule of law issues, said piracy remained an area of concern.

Washington would "like to see continuing improvement in the area of intellectual property enforcement," he told reporters.

Software companies who have done business in China for years "haven't yet seen an uptick in software sales," even though China has touted that all central government agencies are using legally purchased software as of May, Kerry added.

"The recent special campaign was effective at raising awareness, but these efforts need to continue," he said. "They need to deepen the audits of Chinese government agencies and state-owned enterprises."

Chinese piracy and counterfeiting of U.S. software and a wide range of other intellectual property cost American businesses alone an estimated $48 billion and 2.1 million jobs in 2009, the U.S. International Trade Commission said in May.

($1 = 6.443 yuan)

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