The investigation into how armed gunmen were able to kill dozens in a luxury shopping centre in central Nairobi has focussed attention on the militant group al-Shabaab, and its recruitment channels.

ITV News tracked down the preacher Abubaker Shariff Ahmed, who is accused of being the group's top recruiter, in Kenya's coastal city Mombasa.

He said he has nothing to tell police, and also claimed he has never met Samantha Lewthwaite - the British woman who is now the subject of an international arrest warrant.

Read: Who is Samantha Lewthwaite? The woman dubbed the 'White Widow'

ITV News' Africa Correspondent Rohit Kachroo reports:

Read: Worldwide hunt for British 'White Widow'

Kenyan politicians visited the site of the attack today and vowed to establish whether intelligence agencies were asleep on the job.

It follows claims that they received warnings that the shopping centre was a potential target for terrorists.

Read: Al-Shabaab militants claim to be behind Kenyan siege