The United States said that its embassy and consulates in China would not stop tweeting reports on air quality readings in Beijing and Shanghai, which have annoyed the Chinese authorities.
"This is an initiative by the embassy in Beijing, by the mission in China, to convey what we believe is useful information to our citizens abroad," State Department spokesman Mark Toner told journalists.
"It's primarily directed to American citizens, but in terms of Chinese accessing this information, we don't have a problem with it.
"We would see it as a model for other missions around the globe to do," Toner said, adding in the past there had been a similar initiative in Mexico.
He added that despite Beijing's assertions that it was illegal for foreign embassies to issue their own air quality readings the US embassy had no plans to stop sending out the reports on its dedicated Twitter feed.
China's cities are among the world's most polluted, but until recently, official air quality measurements regularly rated their air quality as good -- even as data from the US embassy in Beijing showed off-the-chart pollution.
Toner said the Beijing embassy now had some 20,000 followers of its Twitter feed which goes by @BeijingAir, and which said early Thursday that the air quality was "unhealthy for sensitive groups" in the Chinese capital.
Beijing announced earlier this year it would change the way it measured air quality to include the smaller particles experts say make up much of the pollution in Chinese cities, after a vocal campaign.
"The monitoring and publishing of China's air quality are related to the public interests and as such are powers reserved for the government," Wu Xiaoqing, vice minister of environment protection, told reporters Tuesday.
Wu did not name the US, but called on embassies to abide by China's laws, saying publishing their own air quality data was "not in accordance with the Vienna Convention on Diplomatic Relations."
Toner denied on Tuesday that publishing US air quality readings was in violation of the Vienna Convention as far as he was aware. He also said that Washington would have no problem if Chinese embassies wanted to start monitoring air quality in the US capital and sending out their own reports.