LONDON, July 23, 2011 (AFP) - Britain's Queen Elizabeth II has written to King Harald V of Norway to express her sadness over twin attacks that killed 91 people, describing them as an "atrocity", Buckingham Palace said Saturday.

"I am deeply saddened and shocked by the tragic loss of life of so many people on the island of Utoeya and in Oslo," the queen wrote in her message.

"Prince Philip joins me in extending our heartfelt sympathy to Your Majesty and the people of Norway. Our prayers and thoughts are with everyone who has been affected by the dreadful atrocity."

British Prime Minister David Cameron said he was outraged by Friday's "evil" shooting spree at a youth camp and the government headquarters, Norway's deadliest post-war tragedy.

Norwegian police said they were questioning a Christian fundamentalist Saturday over the attacks. He was widely named by the local media as Anders Behring Breivik.

Britain has experienced attacks from different extremist groups in recent years, from nail bombings in London targeting ethnic minorities and gays in 1999 by a former far-right activist to Islamist bombings of London's transport network in July 2005.