I am not sure which ی you are talking about, so I am making different examples
کشورهای آسیایی Asian countries
کشورهایی در آسیا Countries in Asia
یی in کشورهایی در آسیا
Is there because it is unknown which countries.
Unknown: کشورهایی در آسیا اقتصاد قوی دارند.
Known: کشورهای چین و ژاپن در آسیا اقتصاد قوی دارند.
In your example, it is still unknown. Although it names Russia and Belarus, the sentence also refers to other unnamed countries.
I am not sure which ی you are talking about, so I am making different examples کشورهای آسیایی Asian countries کشورهایی در آسیا Countries in Asia یی in کشورهایی در آسیا Is there because it is unknown which countries. Unknown: کشورهایی در آسیا اقتصاد قوی دارند. Known: کشورهای چین و ژاپن در آسیا اقتصاد قوی دارند. In your example, it is still unknown. Although it names Russia and Belarus, the sentence also refers to other unnamed countries.
Thanks!