China has formally arrested an Australian citizen who was formerly a news anchor for Chinese state television, escalating a case that has contributed to tensions between Beijing and Canberra.

Cheng Lei, a Chinese-born Australian who most recently worked for state broadcaster CGTN, was formally arrested in China on Friday following six months of detention, the office of Australian Foreign Minister Marise Payne said in a statement Monday. Chinese authorities have advised that Cheng was "arrested on suspicion of illegally supplying state secrets overseas,” the statement said.

China had said in September that Cheng was "suspected of carrying out criminal activities endangering China’s national security,” among the most serious allegations ever brought against a foreign journalist based in the country.