US technology giant Apple is suing a Chinese government agency and a domestic company over patent rights for its "Siri" personal assistant, the official Xinhua news agency said Monday. Apple launched the case against the State Intellectual Property Office, which is in charge of patent rights protection in China, and Shanghai's Zhizhen Network Technology, which developed software similar to Siri, the report said. Apple declined to comment to AFP, saying it does not comment on any ongoing litigation. The US company previously asked the State Intellectual Property Office to declare Zhizhen's voice recognition patent invalid but the request was declined, prompting the legal action, Xinhua said. The Beijing Number one Intermediate People's Court will hear the case on Thursday, it added. Last year, Zhizhen itself accused the California-based technology giant of copying its "Xiao i Robot" software, which it patented in 2004, to develop Siri. The case was heard by a Shanghai court in July, state media have reported, but no ruling has been announced. Siri, described by Apple as an "intelligent personal assistant", made its debut with the release of the iPhone 4S in 2011 and responds to a user's commands through voice recognition software. Zhizhen claims its product works in a similar way and has wide application in areas including telecommunications, finance and e-commerce. Apple chief executive officer Tim Cook said in January last year that he expected China to become his company's largest market, though he gave no timeframe. Its revenue in Greater China -- which includes Hong Kong and Taiwan -- reached $5.7 billion for the fiscal quarter ending in September 2013, up 24 percent from the previous quarter, according to the company.