The Organisation for Cooperation Between Railways (OSJD or ОСЖД) approved Afghanistan Railway Authority’s request for membership on 6 June 2014, with Afghanistan becoming the 28th country to join.

The XLII session accepted the application of the Government of the Islamic Republic of Afghanistan for OSJD membership and accession to the SMPS and SMGS Agreement.
Source: XLII session of OSJD Ministers (Vilnius, 3 – 6 June 2014), UIC eNews No.404, 17 June 2014

OSJD was established in 1956 to promote technical co-operation and provide a common legal framework to facilitate international passenger and freight transport between member states. Its members are mostly in the former USSR and Eastern Europe, and also include Iran, China, North Korea, Vietnam and Cuba (presumably there is not much through-running to Cuba).

The Intergovernmental Organisation for International Carriage by Rail (OTIF) does similar things in western Europe and beyond; some countries are members of both OSJD and OTIF (if you think this is a confusing acroynm-fest, note that at the XLII session of OSJD Ministers, UIC, CCTT and OTIF all signed MOUs with OSJD…).

In order for Afghanistan railways to connect and integrate with regional and international rail networks, the Afghanistan Railway Authority must align its policies and regulations with that of regional and international organisations such as the International Union of Railways (UIC), Organisation for Carriage of International Freight by Rail (OTIF) and the Organisation for Cooperation between Railways OSJD.
Source: Afghanistan’s Membership to the Organization for Cooperation of Railways (OSJD) Ministry of Public Works/Afghanistan Railway Authority, 25 June 2014

The Afghanistan Railway Authority joined the International Union of Railways (UIC) at the end of 2013.