British prison officers have been warned to be on the lookout after a hostage drama blamed on extremist Muslim inmates, British newspapers reported Wednesday, a sign of simmering tension a week after an off-duty soldier was killed in a frenzied attack on a London street.

An email circulated to high-security prisons and young offenders' institutes warned that Sunday's incident at Full Sutton detention facility in the northern England region of Yorkshire was linked to religious extremism and warned of an increased risk of attacks at other institutions, according to papers including The Yorkshire Post and The Times.

"Three Muslim prisoners took an officer hostage in an office. Their demands indicated they supported radical Islamist extremism," the letter was quoted as saying. "All staff are reminded to remain vigilant to the increased risk of potential attacks on prison officers inspired by these and last Wednesday's events."

The hostage-takers demands have not been disclosed. Britain's Ministry of Justice declined to comment.

The hostage taking — which injured two prison officers — followed the gruesome attack on Lee Rigby, a 25-year-old drummer with 2nd Battalion The Royal Regiment of Fusiliers, who was attacked by two men with knives and meat cleavers last Wednesday near his barracks in southeast London. The murder was made all the more horrifying by a bystander's video which appeared to show one of the chief suspects with bloody hands, lambasting the British government and the presence of U.K. troops in foreign lands.

The English Defense League, a right-wing group with strong anti-Islam leanings, has mounted a series of protests in the wake of the killing, while Muslim community organizations have reported a surge in attacks and harassment. One mosque in the northern England town of Grimsby was firebombed, while the word "ISLAM" was daubed in big red letters across the Royal Air Force Bomber Command memorial in London's Green Park, near Buckingham Palace.

Two people have been charged over the arson attack. It's unclear who was responsible for the graffiti.

Hackers have gotten in on the act too, with the Anonymous collective of Internet rebels posting a purported list of English Defense League leaders and supporters to the Web.

The list was at least partially genuine, according to English Defense League supporter Glen Warren, 32, whose name and phone number were among those made available online. He said Anonymous appears to have spliced together old information leaked by a disgruntled supporter with newer information gleaned from Facebook postings and media reports.