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.