Much of southern Somalia is controlled by Al-Shabaab
The home secretary is to designate the Somalia-based group Al-Shabaab as a terrorist organisation and ban its operation in the UK.
The Home Office says the group is committed to violence, deploys terror tactics and has been implicated in attacks on Somali citizens.
Last month the group released a statement linking itself for the first time with Al-Qaeda.
Home Secretary Alan Johnson said that the ban was "tough but necessary".
He added that proscription was "not a course of action we take lightly".
The ban would mean that membership of Al-Shabaab in the UK becomes a criminal offence and it could not operate lawfully, for example by fund-raising.
An order has been laid in Parliament which is subject to Parliamentary approval.
If passed, membership will be punishable with up to 10 years in prison.
Much of southern Somalia is controlled by Al-Shabaab.
In a statement released in February, the group said that the "jihad of Horn of Africa must be combined with the international jihad led by the al-Qaeda network".
Recently, Mr Johnson has also banned Islam4UK, the group run by al-Muhajiroun founder Anjem Choudary, and which had threatened to march through Wootton Bassett, Wiltshire.