Google's accused the Chinese government of blocking its Gmail service, making it difficult for local users to access the site.
People within the country have been complaining in recent weeks that they've had difficulty accessing their accounts or sending email. Even the Person Finder application, set up to help people locate missing relatives in the aftermath of the Japanese earthquake and tsunami, appears to have been compromised.
Google first became aware of the problem a couple of weeks ago. "We’ve noticed some highly targeted and apparently politically motivated attacks against our users. We believe activists may have been a specific target," it said on its security blog.
And Google says it's now checked out the problem thoroughly and confirmed that there's no technical issue on its side. "This is a government blockage carefully designed to look like the problem is with Gmail," it says.
China's already blocking or limiting access to a number of sites, including YouTube, Facebook and Twitter.
It's possible that, once again, the real target is human rights activists. In late 2009, a series of hacking attacks prompted Google to close down its mainland China website and move operations to Hong Kong. The attacks appeared to have been aimed at accessing the Gmail accounts of campaigners.
Google later reopened the site in order to hang on to its operating license in the country.