Samantha Lewthwaite, 29, is wanted on charges of possession of explosives and conspiracy to commit a felony dating to December 2011, Interpol said in a news release announcing a "Red Alert" for the suspect.
The alert, requested by Kenya, was sent to 190 countries that are members of Interpol.
Lewthwaite had previously been wanted only on the national level for alleged possession of a forged South African passport, said the organization's secretary general, Ronald K. Noble.
She is the widow of Germaine Lindsay, one of four people who committed a series of bomb attacks in London in 2005 in which 52 people were killed.
Lewthwaite has been linked to the Somali terrorist group al-Shabaab, which claimed responsibility for the attack on the Westgate Mall in Nairobi on Saturday, the BBC reported.
The alert, which requires member countries to detain her for extradition, does not specify Lewthwaite's connection to the Kenyan attack, although speculative reports have linked her to the incident.
Kenyan and foreign forensics teams searched the Nairobi shopping mall Thursday for bodies that may be buried in the rubble left by the four-day siege by terrorists.
Kenya's interior minister said he does not expect the death toll to rise significantly but Kenya's Red Cross said at least 50 people were unaccounted for, the BBC reported.
Sixty-seven people are so far known to have died.
Meanwhile, Kenya is observing three days of official mourning for victims of the siege that began Saturday when al-Shabaab militants stormed the upscale shopping center, threw grenades and indiscriminately shot at shoppers and employees. Kenyan flags flew at half-staff.
Kenya's counter-terrorism strategy and its disaster response coordination would be reviewed, the BBC said.
Kenyan investigators worked with experts from the United States, Britain, Germany, Canada and Interpol to examine the mall for DNA, fingerprints and ballistic clues.
Interpol will help coordinate the international response, Interpol's Executive Director of Police Services Jean-Michel Louboutin said in a release. It also will help disseminate forensic information, photographs of the suspected terrorists, details of arrested individuals and other suspects linked to the assault, to Interpol's network for comparison against national databases.
"We have moved to the next phase," Interior Minister Joseph Ole Lenku said Wednesday.
Lenku confirmed five militants were dead, saying he expected "insignificant numbers of bodies" would be found beneath rubble after three floors of the multistory mall collapsed, which contradicts the Red Cross' number of those unaccounted-for.
Officials were working to identify the deceased militants, including to determine whether one was a woman.
Lenku said he couldn't confirm whether any British or Americans were involved in the attack, but that 10 people were detained.
Somali Islamist group al-Shabaab, which is linked to al-Qaida, said it had carried out the attack in retaliation for Kenyan army operations against militants in Somalia.