The IAAF has rejected bids from 28 Russians to compete as neutral athletes and approved only three.
Russia was banned in 2015 from all international track and field competition, amid allegations of widespread doping and a cover-up orchestrated by government officials.
Former European javelin champion Vera Rebrik, who competed for Ukraine until 2014, was approved on Wednesday to compete along with 400-metre runner Ksenia Aksyonova and hurdler Vera Rudakova.
In all, 15 Russians have been cleared to compete internationally as neutrals, while the world governing body has rejected 45 others. The 28 who were rejected on Wednesday weren't named.
"I'm grateful to the members of the Doping Review Board for the dedication and diligence they are giving to this ongoing review process," IAAF president Sebastian Coe said in a statement.
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"The importance of this huge task should not be underestimated. There can be no time constraints or deadlines when the protection of clean athletes everywhere is at stake."
The large number of rejections is a blow to Russia's hopes of fielding close to a full track team at August's world championships, even if they're categorised formally as neutrals.
Those already approved include high jump world champion Maria Lasitskene, 110m hurdles world champion Sergei Shubenkov and doping whistleblower Yulia Stepanova, an 800m runner.
Lasitskene recorded the biggest win yet for a neutral athlete at last week's Diamond League meet in Eugene, Oregon, leaping 2.03 meters to take first place in the high jump.
Another 27 cases remain under review, the IAAF said.
Meanwhile, six Russian and Ukrainian track athletes have been handed doping bans after retests found they had doped at the 2008 and 2012 Olympics.
The IAAF says Russian sprinter Yulia Chermoshanskaya, who won relay gold in 2008, was banned for two years. Two Ukrainians, javelin silver medallist Oleksandr Pyatnytsya and pole vault bronze medallist Denys Yurchenko, were also banned for two years.
They had already been stripped of their Olympic medals last year.
There were also two-year bans for Ukrainian athletes Vita Palamar, Marharyta Tverdohlib and Maksym Mazuryk.
The IAAF also announced an eight-year sanction for Nataliia Lupu, who was the 800m European indoor champion in 2013. The IAAF says the Ukrainian failed a test in July, her second offence.
