A years-long war between Google and China that highlights the ideological chasm between the two behemoths has now entered a new phase. On Monday morning, reports confirmed online chatter that Gmail has been fully blocked in China. And transparency advocates say they know exactly what’s to blame: China’s Great Firewall.

“I think the government is just trying to further eliminate Google’s presence in China and even weaken its market overseas,” an anonymous representative of GreatFire.org told Reuters. “Imagine if Gmail users might not get through to Chinese clients. Many people outside China might be forced to switch away from Gmail.”

The latest move, which Internet analysis firm Dyn Research also said is the work of the Chinese government, is only the latest in a months-long campaign to break what little hold Google still has in China. Using Google in China has long been tedious, sluggish work. But in June, before the Tienanmen Square crackdown anniversary, accessing it got harder.

“In an effort to prevent the dissemination of information related to this event, the Chinese censorship authorities have severely blocked most Google services in China, including search and Gmail,” Greatfire.org, a Web site that monitors the Internet in China, told Bloomberg News. “Our gut feeling is this disruption may be permanent.”

That gut feeling may be right. Until late last week, those with Gmail accounts could still access their e-mail using third-party e-mail apps like Microsoft Outlook or Apple Mail. But then, suddenly, that ceased to be an option as well.

On Dec. 26, Google’s real-time Transparency Report showed Gmail traffic dropped to nearly zero. “We’ve checked and there’s nothing wrong on our end,” a Singapore-based spokesman for Google told Reuters.

So that leaves few suspects beyond direct, Chinese intervention. “China has a number of ways they can block content,” Earl Zmijewski of Dyn Research told Mashable. “One of the crudest ways is to just block an IP address, and when you do that, you block all the content available at the IP.”

China wields the world’s most powerful Internet muzzle, called the Great Firewall of China, and some critics fear the government may be creating an Internet untouched by the outside world. China first disrupted Google services in 2009 and 2012, amid Google’s warnings it would pull out of the country outright in the name of free speech.

“We have decided we are no longer willing to continue censoring our results on Google.cn,” Google wrote in a lengthy blog post. “…We recognize that this may well mean having to shut down Google.cn, and potentially our offices in China.”

Since then, activists say China has done everything it can to run Google out of town — though Chinese authorities haven’t taken credit for the recent Gmail shutdown. A Chinese Foreign Ministry spokesman told Reuters she didn’t know anything about the Gmail block.

“China has consistently had a welcoming and supportive attitude towards foreign investors doing legitimate business here,” she told Reuters. “We will, as always, provide an open, transparent and good environment for foreign companies in China.”