A British national has been arrested in Nairobi over the bloody attack on a shopping mall by armed Islamists, a spokeswoman for the Foreign Office said on Wednesday.

"We can confirm the detention of a British national in Nairobi and we are making contact to offer standard consular assistance," she told AFP, without saying if the suspect was a man or a woman.

British newspapers have speculated that Samantha Lewthwaite, the widow of one of the men who bombed the London transport system in 2005, was among the attackers who besieged the Westgate mall in the Kenyan capital.

Kenyan Foreign Minister Amina Mohamed told US television on Monday that a British woman was among the attackers, although this contradicted earlier statements from Kenyan officials who said they were all male.

Lewthwaite, a 29-year-old Muslim convert known as the "White Widow", has been on the run in East Africa for the last couple of years and is wanted by Kenyan police for alleged involvement in a separate terror plot.

President Uhuru Kenyatta announced an end to the 80-hour bloodbath in Nairobi late Tuesday, with the loss of 61 civilians and six members of the security forces.

He said five attackers were killed and 11 suspects detained.

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