The Foreign Correspondents Club of China said on Friday it had shut its website after a burst of hacker attacks, days after attacks on the Yahoo email accounts of some foreign journalists covering China were discovered.

We do not know who is behind the attacks or what their motivation is, the club's board said in an emailed statement explaining it had decided to shut down temporarily the site after two days of persistent attacks.

The club has traced the online assault to IP addresses in both China and the U.S., but added that these machines could have been taken over by hackers in other locations.

The hacking was the latest of several recent incidents that have brought to light the Internet vulnerabilities of people or groups whose work may raise hackles in China.

Yahoo email accounts of some journalists and activists whose work relates to China were also compromised in an attack discovered this week, with some users still shut out from their accounts, rights groups and foreign correspondents said.

Google's recent decision to move its Chinese-language search services out of China came after the company discovered it had been the victim of a sophisticated cyber attack originating from China, and found that the Gmail accounts of dozens of activists connected with China were being compromised.

China's government has said it condemns Internet hacking and was not behind the attacks on Google. Some analysts, however, say such attacks have the hallmarks of a sophisticated organization.