Interpol said this is the first time it has been asked to issue a "red notice" for Lewthwaite. The wanted-person alert said she is wanted on charges of possessing explosives and conspiracy to commit a felony in December 2011.
There was no immediate explanation from Kenyan police on why it asked for the alert now.
"Kenyan authorities have ensured that all 190 member countries are aware of the danger posed by this woman, not just across the region but also worldwide," Interpol said in a statement.
Lewthwaite, the daughter of a former British soldier, was born in Northern Ireland and grew up in Aylesbury, a commuter hub northwest of London.
She converted to Islam - reportedly while in her teens - and went on to study religion and politics at the School Of Oriental and African Studies in London. It was around that time she met Lindsay, first in an Internet chat room and later at a London demonstration against the war in Iraq.
The coupled married in an Islamic ceremony in 2002 and moved back to Aylesbury a year later.
Local City Councilor Raj Khan, who knew Lewthwaite in her early teens and ran into her again shortly before the subway bombings, told The Associated Press she was a "normal, average British girl" who was shy and lacked confidence.
"She was going through the journey of becoming a Muslim," he said. "There was no sense of radicalization, and no feeling among people that she showed signs of radicalisation."
Khan said he lost touch with her for about 10 years and met her again after she married Lindsay. The couple approached him and asked if he could help them find subsidised housing.
"She seemed the same soft-spoken girl, becoming a mature young lady," he said. "I asked them to come see me in my office in the next three or four weeks, with the relevant documents, and the next thing I knew was the 7/7 bombings. After that she went into obvious hiding. No communication was made."
He said he thinks of her as a follower, not a leader.
"How these people could have turned him and poisoned his mind is dreadful," she was quoted as saying. "He was an innocent, naive and simple man. I suppose he must have been an ideal candidate. He was so angry when he saw Muslim civilians being killed on the streets of Iraq, Bosnia, Palestine and Israel - and always said it was the innocent who suffered."
After that, she stayed largely out of view until March 2012, when her name surfaced in a Kenyan terrorism investigation.
Kenyan officials said at the time that Lewthwaite and other foreigners travelled to Kenya in 2011 to plan a bomb attack on the Kenyan coast over the Christmas holidays.
Authorities said Lewthwaite, who at the time was pregnant by her new Kenyan husband, was in charge of finances for the planned attack, and they suspected she had rented several houses in Mombasa to assemble a bomb.
Detonator caps and bomb making materials similar to those used in the London transit attacks were found in a house she shared with an accomplice, according to officials. The group was allegedly collaborating with Kenyans sympathetic to al-Shabab.
In December 2011, Kenyan anti-terrorism police found a woman they believed to be Lewthwaite in the house, but they let her go after she showed them a South African passport.
Police later realised the passport was fraudulent, but by the time they returned to the house, she was gone.
Valentina Soria, a security analyst and al-Shabab expert with IHS Janes, noted that Lewthwaite's name has popped up after nearly every terror episode in East Africa over the past two years. She said Lewthwaite has long been an object of fascination as a white woman alleged to be working for al-Shabab.
Still, Soria was sceptical Lewthwaite could be a mastermind in the al-Qaeda-linked group - or one of the fighters in the mall, since using female attackers is not al-Shabab's way of operating.
Lewthwaite's real value, Soria said, could be in recruiting: "It may have been an advantage for al-Shabab to have a personality like that linked to the group - because of the kind of example she could represent in terms of attracting Western recruits."
- AP
