BEIJING -- Pro-Tibet activists said Wednesday they have been bombarded with abusive phone calls and virus emails as they try to contact witnesses in Tibet and nearby amid a clampdown following anti-Chinese riots.

Matt Whitticase, from the Free Tibet Campaign, said he had received calls every two minutes from 4:00 am to 7:00 am Tuesday in London to his mobile number and also at his work number.

"Of course I have no way of saying who the calls were from, but a variety of callers (from British mobile numbers) had Chinese accents," he said in an email.

"The content was crude, abusive and highly anti-Tibetan in nature. The calls also contained the sort of patriotic Chinese music you used to hear on Chinese trains and in public places.

"It seemed that the intention was to stop me from working and from making calls."

Lhadon Tethong, director of Students for a Free Tibet, told AFP that their New York office had also received abusive calls from people speaking Chinese, and added that they had received viruses via email.

"We are getting virus attacks that are just shameless... claiming to be desperate people inside Tibet. The emails are well-written and emotional, pleading for us to open the images," she told AFP.

Tashi Choephel, a researcher at the India-based Tibetan Centre for Human Rights and Democracy, said their email system was unusable because of attacks.

"At the moment we are having to use outside emails because our email accounts are not working, we have to direct everything through our outside emails," he told AFP.

Choephel said the centre had also received an anonymous phone call from Hong Kong trying to find out the source of photos they sent had published apparently showing Tibetan protesters with gunshot wounds and other severe injuries.

One other group, which did not want to be identified, told AFP its computers had been compromised by virus attacks over the last few days.

AFP received an email Tuesday from someone claiming to be in Denmark, who had attached a file they said were pictures of Tibetans shot by the Chinese army. When AFP tried to open the attachment, a virus warning appeared.

The groups are trying to contact people inside Tibet and the surrounding regions to try to find witness accounts of deadly violence that has erupted there in the past few days amid anti-Chinese protests.

Journalists, rights groups and activists are being prevented from gaining access to almost every part of China where protests are reported to have taken place.