World indoor 1500m champion Abeba Aregawi has been provisionally suspended after testing positive for a banned substance.
The Ethiopia-born Swede, 25, failed an out-of-competition test conducted by governing body, the IAAF.
Aregawi, who won gold at the 2013 World Championships in Moscow and 2014 World Indoor Championships in Sopot, has requested a B sample be tested.
Britain’s Hannah England finished fourth behind Aregawi in Moscow. There is no suggestion Aregawi’s performance in that race is under scrutiny.
Aregawi ran for Ethiopia at the 2012 London Olympics but began competing for Sweden later that year after being granted citizenship.
She was due to defend her title at next month’s World Indoor Championships in Portland, Oregon.
Her suspension also means her place in the Swedish team for the Rio Olympics in August is in doubt.
The Swedish Olympic Committee (SOC) has already withdrawn its financial support for Aregawi.
“The situation regarding her place on the Olympic team is in quarantine as we wait for the result of the B test,” added SOC chief executive Peter Reinebo.