Kenyan security forces were seen near the site of an attack at an upmarket hotel and office complex in Nairobi, Kenya (Picture: PA).
A member of the SAS is believed to have helped secure a luxury hotel complex in Nairobi after 21 people, including a British man, were killed in a militant attack.
The British man has been named as Luke Potter, programmes director at international development charity Gatsby Africa.
Security forces in Kenya were called into to help end an armed siege by Islamist militants, Al-Shabaab, in Nairobi which began on Tuesday afternoon.
Announcing the end of the operation to secure the area on Wednesday, Kenyan president Uhuru Kenyatta said: "All the terrorists have been eliminated."
It is understood a member of the SAS was involved in the mission, although the Ministry of Defence (MOD) said it does not comment on Special Forces.
Images showed a heavily-armed man with a military vest and balaclava working with local forces and helping victims leave the complex.
It was reported the lone SAS member was involved in the operation, along with US Navy seals, having been in the country to train Kenyan Special Forces.
Security forces were sent into the hotel to flush out the gunmen and the Interior Ministry said the area had been secured on Tuesday night.
However, gunfire and another explosion were later reportedly heard at the scene.
During the night, more than a hundred civilians were taken to safety.
On Wednesday morning, the National Police Service said the area remained "under an active security operation" and ordered people to stay away "until it is declared safe".
A UK Foreign Office spokeswoman said:
"We are in contact with the Kenyan authorities who are coordinating a response and stand ready to assist as required."
Video: Craig Stark speaks to Forces News.
Former US Army doctor, Dr Craig Stark, helped treat casualties following the incident.
Dr Stark, who now works for a company which has hospitals across the continent, was in Nairobi for work. He told Forces News: "One of our hospitals is in Nairobi and happened to be in the vicinity of the attack.
"When we heard what was going on, my team and I showed up at the hospital and we knew we'd be receiving casualties, so we set our mass casualty plan into effect and mobilised the doctors, nurses and technicians and waited for the first casualties to come in.
"My experience is as a US Army doctor and a flight surgeon, so I have a lot of experience in disaster response, international health.
"Even though it's been many years since I left, the training that you get in the military immediately comes back to you and when that mass casualty occurs, your training kicks in and you know what to do."
The Kenya Red Cross said it was helping families searching for loved ones missing since the attack began.
The British Army Training Unit in Kenya (BATUK) has a permanent base in Nanyuki, around 120 miles from Nairobi, with a smaller element in the country's capital.
The unit consists of around 100 permanent staff and a short tour cohort of 280 personnel, according to the MOD.
Under an agreement with the Kenyan government, up to six infantry battalions per year carry out eight-week exercises in the country, along with Royal Engineer exercises and medical deployments.