A British woman and "two or three" Americans are thought to be among the militants who have killed at least 62 people, including three Indians, at a swanky shopping mall in Kenyan capital of Nairobi.
Kenya's Foreign Minister Amina Mohamed has said the woman had "done this many times before" and "two or three" Americans were also among the attackers.
Six British nationals are confirmed dead in the attack on the Westgate mall in Nairobi and there are conflicting reports over whether the siege has ended yet.
The United Kingdom Foreign Office said the next of kin of the six had been informed and were being offered consular support.
Mohamed's comments will fuel speculation that British terror suspect Samantha Lewthwaite, who was married to 7/7 London bomber Jermaine Lindsay, may be the Briton involved.
Lewthwaite, dubbed the 'White Widow', is known to be in East Africa and is wanted by Kenyan police over alleged links to a terrorist cell that planned to bomb the country's coast.
In March last year, officials said she had fled to Somalia and officers were hunting a woman who used several identities, including hers.
Responsibility for the attack has been claimed by Al Shabab -- an Islamist group based in neighbouring Somalia, which is part of the Al Qaeda network.
At a press conference in Pakistan, British Home Secretary Theresa May said, "I am aware that there have been reports of a British woman being involved, but until we have seen the investigations completed, it is not possible to give further details to confirm or deny that issue."
Meanwhile, Kenyan troops continued to battle the extremists in the deadly shopping mall siege today -- the fourth day of the attack.
"We continue to liaise very closely with the Kenyan authorities and to support their investigation into this attack," a army spokesperson said.
Britain's security service MI5 is reportedly trawling records of Britons with links to extremists in Somalia amid concerns that sympathisers could follow up the shopping mall massacre in Kenya with terror attacks in the UK.
Image: Security forces round up suspects outside the mall ' Photograph: Reuters