SHANGHAI — On July 5, officials from China’s Ministry of State Security took four employees of the Anglo-Australian mining giant Rio Tinto into custody here.

Rio Tinto was not told what happened to the employees; neither were their families. One of the four was a high-ranking executive and an Australian citizen. But the Australian government was also in the dark.

A few days later, only after Rio Tinto had issued a public statement that said the company did not know why the four had been detained, did an answer come from Beijing: they were being held on charges of stealing state secrets, spying on China and harming the country’s interests.

The allegations, which may be rooted in a pricing dispute, have rocked the global iron ore industry, strained China-Australia relations and could have a chilling effect on foreign businesses doing deals in China. Companies with operations here have been closely watching the case.

“It is a concern for Australians and other foreign businesspeople working in China that this could happen,” Chris Bowen, Australia’s financial services minister, said Sunday on Australia Channel 10’s “Meet the Press” program.

“It should also be a concern for the Chinese government,” he said. “If foreign businesses feel that the degree of uncertainty is high, it will change the way that foreign businesses around the world approach business in China and approach the placement of executives in China.”

Foreign lawyers here said China’s behavior might also invite retaliation, hurting efforts by Chinese companies to invest abroad. Steve Dickinson, a lawyer for Harris & Moure PLLC, said Sunday in a telephone interview from Qingdao that the Rio Tinto case was likely to slow or stall Chinese corporate expansion plans not only in Australia but perhaps the United States and Europe.

Australian officials have complained about the detentions (three of those held are Chinese citizens), and the lack of formal charges. Over the weekend, Australia’s minister of foreign affairs, Stephen Smith, asked for more details on the case.

Analysts now say they believe the detentions are tied to an increasingly contentious business quarrel over the price of iron ore, an essential steelmaking ingredient and therefore crucial in China’s rapidly ascendant economy, affecting everything from housing costs to auto prices.

Legal experts say that may be why Beijing says the case involves state secrets.

As the world’s biggest consumer of iron ore, China is highly dependent on mining companies like Rio Tinto, which in the past decade have amassed huge profits in China. That dependence, analysts say, has rankled China’s huge state-controlled steel industry.

“Chinese steel mills feel vulnerable,” said Jim Lennon, a London-based steel analyst at Macquarie Group. “They are the growing demand in the world. They want to lock in sources of supply. And yet, in the worst ever economic downturn, the annual benchmark price is the second-highest it’s ever been.”

Beijing has not said the detentions are tied to iron ore negotiations. But last Friday, China’s state controlled media said investigators had evidence that the Rio Tinto employees had passed confidential documents that would have given the company an edge in the negotiations.

“China’s meeting memos were secretly leaked to Rio Tinto,” The Economic Observer, a state-controlled Chinese newspaper, reported Friday. “That included China’s bottom-line iron ore price and every steelmaker’s inventory, production cost, schedule and manufacturing details.”

The arrests of the four employees came just weeks after China and the three big iron ore producers — Rio Tinto, BHP Billiton and Vale Do Rio Doce of Brazil — failed to reach an agreement on a price for long-term supplies. Stern Hu, the Australian executive detained by China, was one of Rio Tinto’s top price negotiators.

This year, Chinese steel mills had been seeking a 40 to 45 percent cut from a year earlier. But seeing an economic recovery in sight, producers offered China the same 33 percent cut given to Japan. China rejected it. Now, the price of iron ore is climbing, and China’s steel mills are being forced to pay a higher price.

Chinese steel executives feel particularly aggrieved because they agreed last year to an increase of up to 97 percent and then watched prices tumble with the global economy.

“This year, on the China side, the sentiment during the negotiations was soured by last year’s huge loss,” said Zhou Xizeng, a steel analyst at CITIC Securities. “So China brought that irritation to the negotiation table, and they expected a much lower price.”

This is the way it has gone in recent years as China has been forced to pay for its voracious demand for raw materials.

Faced with these soaring costs, China has moved aggressively to acquire assets or invest in overseas mines in Africa, Latin America, Australia and elsewhere. Few resources are as vital to China as iron ore. But because 70 percent of the iron ore China imports comes from the three companies — Rio Tinto, BHP Billiton and Vale — Beijing has sought to devise a strategy to ensure cheaper supplies.

One way was to group steel mills together as a negotiating bloc. Another way was to play spoiler.

In 2007, when BHP Billiton tried to merge with Rio Tinto, Beijing raised objections and worried about an even greater concentration of market power (Rio Tinto rejected BHP’s bid).

Then early last year, Chinalco, a big Chinese company, sought to acquire a stake in Rio Tinto. Later, when Rio’s fortunes soured with the global economy, Chinalco sought a larger stake.

The entire deal was scuttled last month, however, after a growing number of Australians worried about giving China such control. Instead, Rio Tinto formed an alliance with BHP Billiton, the world’s biggest mining company. Around the same time, Rio Tinto, BHP and Vale took a tougher line in the iron ore negotiations.

In years past, Chinese officials have complained about iron ore producers’ “manipulating the market” and forcing prices higher.

Analysts say China’s Steel and Iron Association, which represents the big steel mills, has repeatedly asked individual mills not to buy from Rio Tinto or other producers during negotiations, giving China an opportunity to secure a deal for lower prices. But time and again, analysts say, China’s own steel makers, desperate for iron ore, buy it anyway.

Some Australian officials have suggested the detention of the four Rio Tinto employees is China’s payback for Rio Tinto’s decision to scrap the Chinalco investment or the breakdown in iron ore talks. Regardless of China’s motive, some experts say the detentions are a public relations fiasco.

“China has been playing the big spender and hoping things would go their way, but things have not gone their way,” said David Kelly, a professor of Chinese studies and the director of the China Research Center at the University of Technology in Sydney. “So some people may be trying to save face because they didn’t nail down the resources they should have nailed down.”