Michael Phelps was among a group of 23 American swimmers who demanded more drugs testing in the run up to the Rio Olympics, the BBC has learned.

The Olympics' most decorated athlete signed a letter sent to the International Swimming Federation (Fina) in December.

It proposed carrying out "at least six" targeted, out-of-competition tests on the 10 quickest swimmers in each of the 34 Olympic events.

Fina accepted the proposal in January.

The tests for a range of prohibited substances include the collection of urine and blood samples and represent a significant increase.

Other US swimmers making the "urgent request" to the governing body included Ryan Lochte and Missy Franklin.

The swimming competition in Rio has been marred by increased tension between competitors after the IOC resisted demands for a blanket-ban of Russia despite the McLaren report into state-sponsored doping.

Seven Russian swimmers have been allowed to compete in Rio after initially being banned, leading to complaints from several rivals.
www.bbc.com/sport/olympics/37059168