Region
Soviet Union --
25
Soviet Union
15
United States --
15
United States
14
Developing countries
3
China --
2
Developing countries --
2
Europe, Eastern --
2
Yugoslavia --
2
Africa
1
Africa --
1
Africa, Southern --
1
Caribbean Area --
1
Europe
1
Former Soviet republics
1
Former Soviet republics --
1
Russia (Federation) --
1
United states --
1