Chinese authorities have given their first indication of why an Australian journalist has been detained in Beijing after two other reporters were questioned and forced to flee the country.
A separate report from China's state-owned media has also raised questions about whether the arrest and interrogations might be part of a diplomatic tit-for-tat.
Cheng Lei, a high-profile business anchor on Chinese state television, has been held in a secret location for more than three weeks.
Videos of her have been removed from Chinese websites.
"The Australian national Cheng Lei is suspected of carrying out criminal activities endangering China's national security," Chinese foreign ministry spokesman Zhao Lijian told reporters.
"Compulsory measures have been imposed on Cheng and she has recently been investigated by relevant authorities."
A report from China's state news agency could provide another possible motive for her arrest.
The Xinhua report alleged Australian intelligence agency staff searched the homes of Chinese journalists in June, questioning them for several hours and removing their computers and mobile phones.
The Chinese embassy in Canberra described the reported raids as "quite concerning".
"We have provided consular support to Chinese journalists in Australia and made representations with relevant Australian authorities to safeguard legitimate rights and interests of Chinese citizens," the embassy told AAP.
The ABC reported the ASIO and AFP raids were part of an investigation into alleged foreign interference linked to former NSW Labor political staffer John Zhang, who was a member of a WeChat group with two Chinese scholars.
The visas of the two Chinese scholars had been revoked, the ABC said.
Mr Zhang has denied any wrongdoing and has launched court action over the investigation.
The ABC's Bill Birtles and Michael Smith from the Australian Financial Review were rushed out of China for their own safety this week, after being banned from leaving until they answered questions about Cheng.
Chinese police told the men they were people of interest in the case and both journalists were ordered to report for questioning.
They sheltered in Australian diplomatic compounds for days as their travel rights were revoked.
Consular officials secured safe passage after the pair agreed to be interviewed.
Both journalists say they are relieved to be home but disappointed about the circumstances surrounding their departure.
Mr Zhao told reporters the questioning of the men was a normal enforcement of the law, which authorities had strictly adhered to during their investigations.
He said China protected the legitimate rights and interests of news gathering staff and they had the obligation to comply with the laws and regulations in China.
"As long as foreign journalists conduct news reporting in accordance with laws, they should have nothing to worry about," Mr Zhao said.
The federal government is advising all Australians not to travel to China, warning they could face arbitrary detention.
Australia has now been left without any credentialed journalists on the ground in China for the first time in 50 years.
"It is disappointing that after many years, Australia will not have a media organisation present in China, for some period of time," Foreign Minister Marise Payne said.
Australian Associated Press