The British woman dubbed the "White Widow" was at the centre of a worldwide hunt on Thursday after Interpol issued an international arrest notice in the wake of the Kenya shopping mall attack.
Samantha Lewthwaite, a 29-year-old Muslim convert, was married to Germaine Lindsay, one of four Islamist suicide bombers who attacked the London transport network in July 7, 2005, killing 52 people.
The Interpol red notice, issued at Kenya's request, says the mother-of-three is "wanted by Kenya on charges of being in possession of explosives and conspiracy to commit a felony dating back to December 2011."
But while it did not specifically mention the bloody four-day mall siege in Nairobi by Somalia's Al-Qaeda-linked Al-Shebab movement -- which ended Tuesday -- it follows widespread media speculation over Lewthwaite's possible role in the massacre.
Kenya's foreign minister said a British woman was among the Westgate Mall attackers although President Uhuru Kenyatta later said the reports could not be confirmed.
Interpol issued four colour photographs of Lewthwaite along with the arrest notice. One shows her with long dark hair and pouting at the camera, while the other three show her wearing the Islamic headscarf in various poses.
The notice said Kenyan authorities wanted other member nations to be "aware of this danger posed by this woman, not just across the region but also worldwide."
It said Lewthwaite had previously only been wanted "at the national level for alleged possession of a fraudulently obtained South African passport."
The Interpol notice requires member states to detain the suspect pending extradition procedures.
An 'average, ordinary' girl
The daughter of a British soldier, Samantha Louise Lewthwaite professed herself appalled when her Jamaican-born husband detonated a rucksack full of explosives and blew himself up on a London Underground train at Russell Square station on July 7, 2005, killing 26 people.
She was pregnant with their second child at the time.
"I totally condemn and am horrified by the atrocities which occurred in London," she said, describing Lindsay as "a good and loving husband and a brilliant father, who showed absolutely no sign of doing this atrocious crime".
Lewthwaite had met Lindsay in an Internet chat forum when she was 17, having converted to Islam two years earlier.
Described as a bubbly teenager, schoolfriends said she had an ordinary upbringing, first in Northern Ireland and then in the market town of Aylesbury, northwest of London.
"She was an average British, young ordinary girl," said Raj Khan, a local councillor who knew the family. "She didn't have very good confidence."
Investigations have begun to lift the veil on Lewthwaite's shadowy movements since the London bombings.
South Africa said on Thursday that Lewthwaite had gained a South African passport using the assumed identity Natalie Faye Webb and the document was cancelled in 2011.
She had first entered the country in 2008.
She was accompanied by her three children, a girl and two boys, who would be now roughly aged between seven and 12.
Media reports this week quoted credit records as showing that "Natalie Faye Webb" had at least three addresses in the South African city of Johannesburg and ran up debts of $8,600 (6,400 euros).
Earlier this month Kenyan authorities accused her of working with another suspected British Islamist, Jermaine Grant, who is on trial accused of links to Al-Shebab and of plotting attacks.
Grant was arrested in December 2011 in the Kenyan port city of Mombasa with various chemicals, batteries and switches, which prosecutors say he planned to use to make explosives.
It is believed Lewthwaite escaped when they arrested Grant although she was never seen.
There is no suggestion she is romantically linked to Grant.
Raffaello Pantucci, a terror expert at Britain's Royal United Services Institute, said Lewthwaite had acquired a "semi-mythical status".
"I don't think we've had any concrete evidence of her being involved in this incident," he said. "But the fact of her being mentioned in this context is not surprising because of her connections."
Nairobi's Daily Nation newspaper quoted security sources saying that extremists on the Kenyan coast call her "Dada Muzungu" - "white sister" in Swahili - and that she had slipped through a Kenyan dragnet in Mombasa in January 2012, when forces raided villas where she was believed to have been hiding.
Rumours abound that Lewthwaite is behind the Twitter handle @MYC_Press -- Kenya's radical Muslim Youth Centre -- which regularly comments on Kenyan extremism, as well as entering into a war of words with rival Islamists.
It has been silent since Saturday, when the Nairobi attacks began.