China's Foreign Ministry said on Monday that a China-based reporter for the New York Times broke rules on residence visas and would be leaving the country before the end of the week, in a case which could sour Beijing's relations with Washington.

The issue of media freedom for foreign reporters in China has attracted high-level concern in the United States, especially over worries that the government is denying visas for organizations that carry negative stories about China.

Last month, U.S. Vice President Joe Biden expressed concern, while on a visit to Beijing, over China's efforts to restrict the activities of foreign news organizations.

Neither the New York Times Co nor Bloomberg News has been given new journalist visas for more than a year after they published stories about the wealth of family members of former Chinese Premier Wen Jiabao and current President Xi Jinping, respectively.

The New York Times applied for a journalist accreditation in China for U.S. national Austin Ramzy in the middle of last year, after he left Time magazine.

Ramzy remained in the country on the visa that he had received while working for Time, which was valid until the end of 2013. Chinese authorities then issued him a 30-day visa, valid until January 30, ostensibly to give him enough time to prepare to leave the country.

Foreign Ministry spokesman Qin Gang said Ramzy informed them in May that he was no longer working for Time magazine and he handed back his government-issued press card, which foreign reporters are required to have to report legally in the country.

"But Austin Ramzy did not, in accordance with Chinese regulations, apply to other Chinese departments to change his visa type and his residence permit type, which previously was for Time," Qin told a daily news briefing.

"Regretfully, Austin Ramzy did not do this, and he continued to use his existing residence permit to come and go from China. So his actions were in contravention of China's rules," he added.

Residence permits in China are contingent upon employment, and foreign nationals are supposed to leave the country when they no longer work for the organization which sponsored their residence permit, or else convert to another visa type.

Ramzy declined to comment when reached by Reuters, and the New York Times did not immediately respond to an emailed request for comment.

"The NY Times, following rules, handed Foreign Ministry a visa application for Austin Ramzy last June. They have not approved it," Edward Wong, acting Beijing bureau chief for the Times, said on Twitter.

Qin said that both the New York Times and Ramzy had admitted to the Foreign Ministry to contravening China's rules, and that the ministry had granted Ramzy a visa valid until the end of January to give him time to sort out personal affairs.

Qin added that the Foreign Ministry was currently handling the New York Times' request for accreditation for Ramzy, but that it would not be completed before January 31, implying that he would have to leave when his visa expires on January 30.

If that happens, Ramzy's case will be the second time in 13 months that a New York Times reporter has had to leave China. Chris Buckley, a former Reuters journalist, had to leave Beijing in December 2012 after the government did not approve his accreditation for the New York Times.

Buckley has not yet received approval to return to China as a resident journalist. He works from Hong Kong.

The newspaper has another outstanding China visa application, for Philip Pan, its Beijing bureau chief in waiting.

Asked whether China would grant journalist visas to either Buckley or Pan, Qin said it was China's sovereign right to decide to whom it granted journalist accreditations and visas.

Foreign reporters working in China face numerous difficulties, including interference, or even violence, when covering sensitive issues such as protests and dissidents' trials. China says foreign media are granted wide-ranging freedoms.

In November, the Chinese government rejected a visa application by Paul Mooney, an American journalist to whom Thomson Reuters had extended an offer to work in China. The government gave no reason for the rejection.