Related Rule
Russian Federation
Practice Relating to Rule 125. Correspondence of Persons Deprived of Their Liberty
The Russian Federation’s Regulations on the Application of IHL (2001) states:
Immediately upon capture, or not more than one week after arrival at a camp, even if it is a transit camp, likewise in case of sickness or transfer to hospital or another camp, every prisoner of war shall be enabled to write to the Central Prisoners of War Agency a card informing them of his capture. Besides he has the right to write to his family and inform them of his capture and state of health. 
Russian Federation, Regulations on the Application of International Humanitarian Law by the Armed Forces of the Russian Federation, Ministry of Defence of the Russian Federation, Moscow, 8 August 2001, § 52.