SYDNEY, Australia (AFP) — Australian Foreign Minister Penny Wong on Tuesday urged the release of citizens held in China, as she prepared to embark on a landmark visit to Beijing.

Wong is set to be the first top Australian diplomat to visit China in four years, a trip aimed at thawing troubled relations.

She will depart Australia on Tuesday for a meeting with Chinese state councilor and minister of foreign affairs, Wang Yi, and indicated before her departure that the issue of the two imprisoned Australians would be on the agenda.

Australian journalist Cheng Lei was detained by Chinese authorities in August 2020, and Chinese-born Australian Yang Jun was detained in January 2019.

Wong said their release would remove one obstacle to improving relations between the two countries.

"I think that it would be beneficial not just for the individuals, which is I think important in its own right, but it would be beneficial to the relationship for those consular matters to be dealt with," she said.

Cheng, a mother of two and former anchor at Chinese state broadcaster CGTN, was formally arrested in February 2021 and charged with "supplying state secrets overseas."

Chinese-born Australian Yang Jun, who also goes by the pen name Yang Hengjun, wrote a series of spy novels and a popular Chinese-language blog. He has been accused by Beijing of espionage and has been tried behind closed doors.

The last official visit to Beijing by an Australian foreign minister was in 2018.

Since then, once-excellent relations have nosedived.

The two countries have sparred over political and moral issues — notably Chinese influence operations overseas; widespread rights abuses in Xinjiang, Hong Kong and Tibet; and America's role in the Asia-Pacific region.

China's Communist leaders were incensed by Australia's decision to effectively ban state-sanctioned firm Huawei from operating the country's 5G network, and by calls from Canberra to investigate the origin of the Covid-19 pandemic.

In retaliation, China quietly slapped sanctions on a range of Australian goods and instituted a freeze on high-level contacts. The frosty relations only ended when Prime Minister Anthony Albanese met with Chinese President Xi Jinping in Bali in November.

Chinese foreign ministry spokesperson Mao Ning on Monday said Beijing hoped Wong's visit would "strengthen dialogue, expand cooperation and keep differences in check, while pushing bilateral relations back on track."

China is Australia's largest trading partner, and Australia still provides many of the ores, metals and minerals that fuel China's spectacular economic growth.