UK Anti-Doping has sent two investigators to Kenya over its "grave concern" about allegations that British athletes took drugs at a training camp.
These doping allegations come from a joint investigation by the Sunday Times and German broadcaster ARD/WRD.
They are the latest episode in the drugs scandal which has rocked the world of athletics and powerhouse track and field nations such as Kenya and Russia in the build-up to the Rio 2016 Olympics.
It is claimed that four unnamed British athletes had been given banned performance-enhancing drugs from Kenyan doctors.
The alleged doping centres around a high-altitude winter base used by international athletes outside Nairobi.
Ukad chief executive Nicole Sapstead, who described the allegations as being of "grave concern and of significant interest" said: "We have opened an investigation and are taking the necessary steps to corroborate the evidence and investigate it further.
"I can confirm that this evidence is being treated with the utmost importance and urgency, and two members of Ukad staff are currently in Kenya pursuing a number of lines of enquiry."
Secret undercover footage shows medics claiming they treated British, Kenyan and other athletes with erythropoietin (EPO), the blood-boosting drug used by sporting cheats such as the disgraced American cyclist Lance Armstrong, according to the Sunday Times.
It also states that Kenya's Directorate of Criminal Investigations arrested three men in connection with the claims.
According to the allegations, two doctors claim to have administered a series of EPO injections to a British athlete shortly before a major race.
The Sunday Times sent undercover reporters to meet the Kenyan doctors in question. They claim to have seen medical notes that one of the Kenyan doctors insists proved he treated a British athlete for an injury.
One of the Kenyan doctors involved is reported to have claimed to have helped 50 athletes take performance-enhancing drugs in the past four years.
Iten plays host to performance camps for many of the world's top athletes, seeking to capitalise on the benefits of training at altitude.
Ms Sapstead said Ukad has "concerns relating to the practices and the lack of anti-doping infrastructure in a number of countries" and urged sports organisations to carry out a risk assessment when choosing where their athletes train.
She said: "We recognise that many athletes train overseas for a number of reasons such as, warmer weather or the altitude, and sometimes in countries which do not have the necessary anti-doping systems in place.
"Whilst ultimately it is an athlete's responsibility to protect themselves from doping, it is absolutely imperative that national governing bodies of sport ensure that their athletes and coaching staff are safeguarded and are training in safe and clean environments.
"They must ensure that they are in the best possible environment to compete, and win, clean."
UKA (UK Athletics) described the allegations as "vague and unsubstantiated", adding that it was confident that top British athletes who trained in Iten were not exposed to doping.
A UKA spokesman said: "To be clear, none of the allegations as presented relating to British athletes accords with our experience.
"Nevertheless, we take any allegations of doping seriously and will as always cooperate fully with any investigation undertaken by Ukad or other anti-doping organisations."
UKA said it believed that "all reasonable measures are taken to ensure the safety and security of our athletes" on its altitude trips.