American Olympic champion Brianna Rollins has been banned for a year for missing three drugs tests in 2016 - one of which came while she was meeting former United States president Barack Obama at the White House.

Another saw Rollins, 25, miss a test to attend 'Brianna Rollins Day' in September in her hometown in Florida.

Rollins, who won 100m hurdles gold in Rio, is banned until 18 December.

She will therefore miss the World Championships in London in August.

"This is one of the most difficult times in my career, especially after having such a great 2016 season," Rollins said in a statement on Instagram.

The United States Anti-Doping Agency (Usada) says Rollins failed to properly file her whereabouts information for drug testers.

Under World Anti-Doping Agency rules, athletes cannot miss three tests in a 12-month period.

Rollins missed one in April 2016, as she was travelling, and two in September - one when she was visiting the White House and the other when she returned to Florida.

Usada says her results from 27 September - the date of her third whereabouts failure - will be disqualified, meaning the world champion will be allowed to keep the Olympic medal she won in August.

"This is a difficult case because it involves the imposition of a serious penalty on a brilliant athlete who is not charged or suspected of using banned substances of any kind," Usada said in the ruling.