BEIJING (AFP) - China rejected mounting foreign complaints about its business environment Thursday, saying it treats all investors equally and that any difficulties are due to increased competition in the huge market. The comments by a government spokesman were the most detailed response yet to charges that China already accused of keeping its currency artificially low was tilting its playing field in favour of domestic companies. In short, the environment for investing in China is getting better, foreign ministry spokesman Qin Gang said. An annual report to the US Congress on Wednesday said China had erected new hurdles to foreign competition with rules favouring domestic firms. The report by US Trade Representative Ron Kirk cited a directive by China stipulating that sellers of high-tech goods must contain Chinese intellectual property for them to be included in a government procurement catalogue. Accredited products will be favoured, according to the policy, which foreign firms say effectively excludes them from the process. Last week, an American Chamber of Commerce in China survey found that 38 percent of members felt unwelcome to participate in Chinas market, up from 26 percent in the fourth quarter of 2009. The survey cited discriminatory government policies and inconsistent legal treatment. But Qin said China was strictly fulfilling its requirements under the rules of the World Trade Organization, which it joined in 2001. He added that if businesses were encountering any problems, it was due to fierce competition in the market. We would like to say one thing to all businesses in China: Congratulations on getting rich, he said. Critics accuse Beijing of keeping its yuan currency undervalued to maintain an unfair trade advantage while the politically sensitive massive US trade deficit with China remains a sore point between the two sides. Concerns about doing business in China were highlighted by the case of four employees of Anglo-Australian mining giant Rio Tinto, including Australian national Stern Hu, accused of bribery and commercial espionage charges. Hu was sentenced this week to 10 years in jail in Shanghai. He and three Chinese colleagues were arrested last year amid contentious iron ore contract talks that later collapsed between top mining companies and the steel industry in China, the worlds largest consumer of the raw material.