""We monitor now very intensively a wide range of Web sites ... Their claim is something we certainly take seriously," Clarke said.
An Internet statement from another group, calling itself the "Organization of al-Qaeda - Jihad in the Arabian Peninsula" praised the attacks and said Rome would be targeted next.
Queen Elizabeth II and her son Prince Charles visited bombing victims at the crowded St. Mary's Hospital yesterday.
"It's been one of the things that many of us have dreaded for a long time," Charles said, speaking to patients injured in the blasts.
"What I can never get over is the resilience of the British people who have set us all a fantastic example of how to recover," he said.
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Premier urges calm after terror attacks in London
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