'Poisonous Narrative'

A combination picture shows the head of the Islamist group al-Muhajiroun Anjem Choudary (L) arriving at Bow Street Magistrates Court in London, in a July 4, 2006 file picture, and Islamist preacher Omar Bakri Mohammed speaking to journalists after his release on bail from a military court in Beirut, in a Nov 24, 2010 file photo. [Photo/Agencies]

The government also said it is forming a group to combat radical Muslim preachers and others whose words could encourage violence.

Prime Minister David Cameron's office said the group aimed to fight radicalism in schools and mosques, tighten checks on inflammatory internet material, and disrupt the "poisonous narrative" of hardline clerics.

Rigby's killing fuelled public anger about radical Islam. It has also raised questions over whether more could have been more to prevent the attack and put pressure on Cameron to tackle suspected militants more forcefully.

Witnesses said the soldier's killers shouted Islamist slogans during the attack. Bystanders filmed one of the suspects saying it was in revenge for Britain's involvement in the wars in Iraq and Afghanistan.

Successive British governments have wrestled with how to prevent people from becoming radicalized without alienating the wider population with draconian measures.

Former British prime minister Tony Blair tried to tighten rules against hate preachers after the London bombings in 2005 that killed 52 commuters. The measures stirred a long debate over how to balance free speech and civil rights with a strong counter-terrorism strategy.  

Britain's two-party coalition government is divided over a planned new law that would allow police and spy agencies to monitor people's use of the internet and mobile phones.

The Muslim Council of Britain, a religious umbrella group, said new government measures risked "making our society less free, divided and suspicious of each other".