China has blocked the last remaining way to access Google's popular e-mail service, Gmail, experts have said, as authorities work to establish "Internet sovereignty" by controlling what enters the country via the web.
Gmail, the world's biggest e-mail service, has been largely inaccessible from within China since the run-up to the 25th anniversary in June of the Tiananmen Square crackdown on pro-democracy demonstrators.
But users could still access the service by using third-party mail applications, rather than the webpage.
There is an increasingly aggressive attitude towards what they (Beijing) call 'Internet sovereignty' and they are confident about talking about Internet censorship in positive terms
"But they have blocked those ways of accessing," said Jeremy Goldkorn, founder of Danwei, a Beijing-based firm that tracks Chinese media and the Internet.
"I think this is pretty confirmed. It is now already four, five days, so this is real," he said.
"There is an increasingly aggressive attitude towards what they (Beijing) call 'Internet sovereignty' and they are confident about talking about Internet censorship in positive terms," Goldkorn added.
State-run media said on Tuesday that Internet giant Google's unwillingness to obey Chinese law was to blame for the shutdown of its email service.
"China welcomes the company to do business on the prerequisite that it obeys Chinese law; however Google values more its reluctance to be restricted by Chinese law, resulting in conflict," the Global Times said in an editorial on Tuesday.
The United States, while careful not to accuse Beijing directly, said it was aware of reports that Gmail had been blocked and that it was "concerned by efforts in China to undermine freedom of expression".
Internet users in China were angry on Monday, with many spewing vitriol on Sina Weibo, a Twitter-like microblogging service.
"The reason for blocking of Gmail domestically is political problems... it reflects the grim situation facing the political environment," one user said.
Another commentator fumed, "Protest the government blocking Gmail! Demand its restoration!"
China operates the world's most extensive and sophisticated Internet censorship system, known as the "Great Firewall".
Foreign websites such as Facebook, Twitter and YouTube are routinely blocked and content that the ruling Communist Party deems offensive is often quickly deleted.
Google withdrew from China in 2010 after a fallout with Beijing over censorship issues.
Access problems could be "caused by the China side, by Google itself or a combination of the two", said the Global Times, which is close to the rulilng Communist party.
A company spokesman told the AFP news agency on Monday that internal check found "nothing wrong on our end".
Chinese foreign ministry spokeswoman Hua Chunying said she was "not aware" of the blocking of the service when asked about the issue at a regular press conference on Monday.
"I would like to stress that China always welcomes and supports foreign investors' legal business operations in China," she said.