The middle-distance runner had been suspended since January 10th after testing positive for synthetic erythropoietin (EPO) in an out-of-competition urine test last October.

Bol's 'A' sample had returned an "Adverse Analytical Finding" but his 'B' sample produced an "Atypical Finding" (ATF) for recombinant EPO, anti-doping watchdog SIA said on Tuesday.

Recombinant EPO is not produced naturally by the human body and is banned by the World Anti-Doping Agency.

SIA said it had lifted Bol's suspension but that the ATF was not the same as a negative test result and it would continue its investigation.

"Sport Integrity Australia will, as part of its investigation, proceed to consider whether any anti-doping rule violation/s have been committed," the anti-doping watchdog said.

"It is not possible to provide a timeframe at this point."

Bol said he had been exonerated.

"Last month I told everyone that I was innocent and asked that everyone in Australia believe me and let the process play out," he wrote on social media.

"I was hopeful the process would exonerate me.

"This morning, I am relieved to report that it did.

"I have never in my life purchased, possessed, administered, or used synthetic EPO or any other prohibited substance, and never will."