British nationals have undoubtedly been caught up in the "callous and cowardly and brutal" Nairobi terror attack which left at least 30 people dead, the Foreign Secretary said.
William Hague said "we should be ready for that and aware of that" as he revealed a rapid deployment team is being sent to Kenya to help in the aftermath of the atrocity at an upmarket shopping centre in the capital.
Somali-based militant group al-Shabaab claimed responsibility for the atrocity in which men armed with guns and grenades stormed the mall and targeted non-Muslims.
Dozens were reportedly being held hostage by the gang in the Westgate Mall, in the affluent Westlands district of the city, which is popular with expats.
Hannah Chisholm, a Briton visiting Nairobi, said she and 60 others barricaded themselves into a large storeroom. She told the BBC: "We kept running to different places but the shots were getting louder so we barricaded ourselves along with about 60 others into a large storeroom. There were children hiding with us as well as someone who had been shot." She added: "The gunfire was loud and we were scared but at that point we thought the gunmen were thieves so we assumed they wouldn't try to reach the storeroom."
Al-Shabaab, also known as Harakat al-Shabaab al-Mujahideen (HSM), appeared to claim responsibility for the atrocity by writing on its official Twitter feed that "the Mujahideen entered Westgate Mall today at around noon".
It said it had previously warned the Kenyan government that if they did not remove military forces from Somalia there would be "severe consequences".
"For long we have waged war against the Kenyans in our land, now it's time to shift the battleground and take the war to their land," it tweeted. "The Mujahideen entered Westgate Mall today at around noon and are still inside the mall, fighting the Kenyan Kuffar inside their own turf."
The organisation claimed it had killed more than 100 Kenyan "kuffar", a derogatory term used to describe non-Muslims.
Nairobi's mortuary superintendent, Sammy Nyongesa Jacob, said Africans, Asians and Caucasians were among the 23 bodies brought in following the attack.