Hundreds of British soldiers will be sent to Somalia to train forces fighting Al-Shabaab.
The Al Qaeda-linked militia have been pushed back from major cities in the war-torn African country after a decade of war.
But security experts claim a resurgence could create a launch pad from where fighters could launch attacks against the West.
In 2015, the group called for attacks on London’s Oxford Street and the Westfield shopping centres.
Prime Minister Theresa May will order up to 900 British troops to Somalia over 18 months to strengthen local forces’ training.
Announcing the deployment yesterday night at the United Nations in New York, the PM May said: “It is vital that as an international community we continue to support countries in the region that are contributing thousands of troops, and that we continue to build the capacity of Somali security forces.
“That is why the UK is now going to increase further our security support, and we will be calling on others to do the same.”
Britain currently has 65 soldiers in Somalia but the new deployments will double their efforts.
Up to 30 teams – each having up to 30 soldiers – will be sent, with no more than 70 troops deployed at any one time.
They will target regions outside the capital city of Mogadishu and will be on a rotation, meaning hundreds will serve over the course of the programme.
They will teach Somali troops to detect roadside bombs – and a British headquarters will be established in Mogadishu.
A No 10 official told The Mirror: “The UK has played a leading role in Somalia.
“Over the last five years we have seen substantial progress in the country, which has reduced the terrorist threat to the UK.
“But our view is that Somalia is now at a crossroads.
“You’ve got a resurgent al-Shabaab, international forces are set to draw down in 2018 and hand over to the Somali forces, parliamentary and presidential elections are due later this year, and we really want to re-energise the international campaign in that context, with the UK continuing to lead efforts.”