Stern Hu, the Australian Rio Tinto executive facing bribery charges in China, has pleaded guilty according to the lawyer for one of his co-accused.Hu, the Anglo-Australian mining giant's iron ore chief executive in China until his arrest, and three Chinese colleagues are accused of illegally obtaining commercial secrets and taking millions of pounds in bribes. According to Bloomberg, the lawyer for Liu Caikiu, one of the four defendants, Hu has pleaded guilty to the charges. The trial started today and is expected to last three days, although the verdicts may take weeks or months to arrive.The trial, part of which is being held in secret, is thought to relate to negotiations over iron ore prices in 2009.China has warned Rio Tinto against politicising the trial.The warning came after Australian Prime Minister Kevin Rudd said the 'world will be watching how this particular court case is conducted' and foreign minister Stephen Smith complained about the absence of Australian officials from parts of the trial that are to be held in private.