Bahrain's Salwa Eid Naser, who ran the third fastest time ever when she won world 400m gold last year, has been provisionally banned after failing to meet 'whereabouts' criteria, the Athletics Integrity Unit (AIU) announced Friday.

The Nigerian-born 22-year-old clocked 48.14 seconds to win the one-lap race at the Doha worlds, placing her third in the all-time top list behind Marita Koch (47.60) and Jarmila Kratochvilova (47.99).

Naser switched allegiance to Bahrain in 2014, when she was 16.