The governing body said Selsouli tested positive for the diuretic furosemide at the Paris Diamond League meeting on July 6.
Selsouli became an Olympic medal favourite after timing 3 minutes, 56.15 seconds in Paris — more than four seconds below her previous personal best.
"Selsouli has waived her right to the B (backup sample) analysis, and as a result has now been provisionally suspended from all competition in athletics," the IAAF said in a statement.
The IAAF said can still request a hearing by the Moroccan Athletic Federation that needs to be held within the next 3 months. The governing body said it will not make any further comment on the case in the meantime.
If found guilty, the 28-year-old runner faces a lifetime ban for a second doping offence of her career.
Selsouli finished serving a two-year ban last August for using EPO before the 2009 world championships.
Furosemide is included on the World Anti-Doping Agency list of prohibited substances. It can also be used as a masking agent to disguise the presence of other performance-enhancing drugs.