BEIJING (REUTERS) - China's Great Firewall just got even higher.

State-run telecom firms are taking on a new filtering role this week in a move that could heavily restrict access to overseas sites.

It is all part of Chinese President Xi Jinping's aggressive campaign to control the country's cyberspace.

Traffic will now be filtered at a much more personal level with telecom companies able to intercept information sent to household modems or mobile phones.

Experts say it could lead to increasing attacks against virtual private networks (VPNs), one of the few tools Chinese users can use to access sites and services from overseas.

VPNs have been the target of continuous attacks by the government as China rolls out new data surveillance and censorship rules.

The latest big Western name to come under fire - WhatsApp. Users have been reporting a series of blocks and delays in the encrypted messaging app.

Researchers also found that messages related to Liu Xiaobo, a dissident and Nobel laureate who died from cancer in custody last week, disappeared from local messaging apps.

But despite the crackdown, the popularity of VPNs is still strong. Some server hosts say their user bases are growing, fuelling a game of cat-and-mouse with the Chinese government, as Beijing regulators race to patch up the holes.