White Widow Samantha Lewthwaite has been behind the murder of at least 400 people, including last month's slaughter of 148 by gunmen at a university in Kenya, Somali security chiefs claimed.

The world's most wanted woman is said to have risen through the ranks of terror group al-Shabaab and now sits "at the right hand of the leader directing attacks".

The 32-year-old former London University graduate, believed to be responsible for car bombings, and terror raids, is also recruiting children and women to become suicide bombers for cash – giving desperate families as little as £300.

"The lady has moved up the ranks. She is one of the most important figures in the terror group," one senior officer at Somalia's National Intelligence and Security Agency, who chose to remain anonymous, told The Mirror.

"She does not carry out attacks herself as she is too important but is responsible for many, many deaths – hundreds.

"She uses children to kill for her after giving money to their families."

But the security forces are getting ready to bring her in dead or alive.

"We share all our information with British agents here in Mogadishu. They are here to keep an eye on the lady and other Britons in Somalia... The SAS are ready to get her or we are ready to call in a drone strike against her. We will get her eventually," said the source.

"We know she has surrounded herself with other Britons, her own people as her Somali language is not so good. They are her lieutenants and bodyguards."

Al-Shabaab has been fighting the Western-backed government and its allies as it fights for Islamic law to be interpreted in the nation.

Lewthwaite was the widow of 7/7 London terrorist bomber Germaine Lindsay, who at the time she portrayed as a loving husband. She has been on the run since December 2011.