China has warned Rio Tinto against politicising the trial of four Rio Tinto executives, which is due to start on Monday.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.One of the four men to go on trial, Stern Hu, is an Australian national. They are charged with bribery and stealing business secrets during negotiations between Rio and China over iron ore prices.The parts of the trial related to charges of obtaining commercial secrets are to be held in private. While consular pacts used to allow diplomats access to trials of the countries they represent, the convention has been scrapped in this case.