A senior Al-Shabaab commander who was the target of an abortive raid by US special forces in Somalia last month had spent time in the UK, the BBC has learned.
Abdikadir Mohammed has been linked to alleged terror plots in Kenya.
Friends have told the BBC that he came to Britain in 2007 and spent time in London, before moving to Somalia the following year.
US Navy Seals failed in an attempt to capture him on 5 October.
The raid followed an attack on the Westgate shopping centre in Nairobi, Kenya, on 21 September that lasted four days and left at least 67 people dead.
Al-Shabaab has claimed responsibility for the siege.
Lewthwaite connection
BBC correspondent Gabriel Gatehouse said it was not clear what role, if any, Abdikadir Mohammed played in that attack.
Abdikadir Mohammed, also known by his alias, Ikrimah, is thought to be a recruiter of foreign fighters, and a key link between Al-Shabaab in Somalia, and al-Qaeda in the Arabian Peninsula, based in Yemen, our correspondent said.
In 2004 he travelled to Norway, where he unsuccessfully sought asylum.
The BBC has discovered that in early 2007 he came to Britain and spent time in London, before moving back to Somalia.
Leaked Kenyan intelligence documents have linked him to Samantha Lewthwaite - the British widow of one of the London 7/7 attackers.
An alleged plot to bomb targets in Kenya was foiled, police say, when they raided a number of addresses in Mombasa in December 2011.
Ms Lewthwaite slipped away, her whereabouts unknown.
Our correspondent said the Kenyan authorities believe apprehending Ms Lewthwaite and Abdikadir Mohammed could help prevent future attacks similar to the one at Westgate.
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Appeal for troops
Meanwhile, UN Secretary General Ban Ki-Moon said an extra 4,500 troops were needed by the UN-backed African Union force fighting Al-Shabaab in Somalia.
Mr Ban said in a report to the UN Security Council that recent military advances against Al-Shabaab could be reversed and there was a danger of more Westgate-style attacks if the 18,000-strong force was not bolstered.
He said that in addition to a troop surge, which would have to be paid for by richer UN member states, the African force also needed military attack helicopters. He appealed to both African and non-African countries to supply these.
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