MPs have agreed to ban a Somali-based group Al-Shabaab after ministers alleged they had links to al-Qaeda.
Policing Minister David Hanson said the group had carried out a string of attacks in the Horn of Africa and had pledged support to Osama Bin Laden's organisation.
The decision to add them to the list of proscribed organisations will prevent Al-Shabaab campaigning or raising funds in the UK and ban people from joining the group.
Mr Hanson told the Commons: "The group has waged a violent campaign against the Somali transitional federal government, has undertaken a violent campaign against the African Union peace troops in Somalia since the beginning of 2007.
"It has undertaken a range of terrorist tactics such as suicide operations and roadside bombings."
The group carried out a car bomb attack in June 2009 which killed the Somali security minister and 30 other people, Mr Hanson said.
Labour's Dari Taylor, a member of the Intelligence and Security Committee, said unless evidence could be tabled "some in our community, with justice, will have concerns that the government is exaggerating the existence of terrorism in Great Britain today.
Mr Hanson said together with Home Secretary Alan Johnson he had decided that the group's activities were "evidence internationally of the intentions of this organisation".
He added: "I can't comment on security matters in this country in detail but we have made the assessment based on our assessment of that information as to whether or not this organisation should be proscribed."
MPs approved the order adding Al Shabaab to the list banned under the Terrorism Act 2000 without a vote.
The order will need to be approved by the Lords before coming into force.