Four-time Tour de France champion Chris Froome failed a drug test during his Vuelta a Espana win in September.

The Team Sky rider had double the allowed level of legal asthma drug Salbutomol in his system.

Cycling's world governing body the UCI has requested more details from Froome and Team Sky.

The Briton, 32, says he increased his dosage but it was within the legal limits and the UCI is "absolutely right" to ask questions.

Froome said he took his team doctor's advice to up his inhaler use after his asthma symptoms got worse during the Vuelta.

He became the first Briton to win the three-week race around Spain and it followed his Tour de France victory in July.

The urine test, taken on 7 September, showed levels of the drug, Salbutamol, which is commonly taken for asthma, were at 2,000 nanograms for millilitre (ng/ml).

That compares to the World Anti-Doping Agency's threshold of 1,000 ng/ml.

No other samples taken from Froome during the competition needed further examination.