The Repatriation Agreement Between the Soviet Union and the United States, Yalta, February 11, 1945.
 (similar agreements also were signed between USSR, Great Britain and France)

Article 1
 All Soviet citizens liberated by the forces operating under United States command and all United States citizens liberated by the forces operating under Soviet command will, without delay after their liberation, be separated from enemy prisoners of war and will be maintained separately from them in camps or points of concentration until they have been handed over to the Soviet or United States authorities, as the case may be, at places agreed upon between those authorities. . ..

Article 2
 The contracting parties shall ensure that their military authorities shall without delay inform the competent authorities of the other party regarding citizens of the other contracting party found by them, and will at the same time take the necessary steps to implement the provisions of this agreement. Soviet and United States repatriation representatives will have the right of immediate access into the camps and points of concentration where their citizens are located and they will have the right to appoint the internal administration and set up the internal discipline and management in accordance with the military procedure and laws of their country.

 Facilities will be given for the despatch [sic] or transfer of officers of their own nationality to camps or points of concentration where liberated members of the respective forces are located and there are insufficient officers. The outside protection of and access to and from the camps or points of concentration will be established in accordance with the instructions of the military commander in whose zone they are located, and the military commander shall also appoint a commandant, who shall have the final responsibility for the overall administration and discipline of the camp or point concerned.

 The removal of camps as well as the transfer from one camp to another of liberated citizens will be effected by agreement with the competent Soviet or United States authorities. The removal of camps and transfer of liberated citizens may, in exceptional circumstances, also be effected without preliminary agreement provided the competent authorities are immediately notified of such removal or transfer with a statement of the reasons. Hostile propaganda directed against the contracting parties or against any of the United Nations will not be permitted.

Article 3
 The competent United States and Soviet authorities will supply liberated citizens with adequate food, clothing, housing and medical attention both in camps or at points of concentration and en route, and with transport until they are handed over to the Soviet or United States authorities at places agreed upon between those authorities. The standards of such food, clothing, housing and medical attention shall, subject to the provisions of Article 8, be fixed on a basis for privates, non-commissioned officers and officers. The basis fixed for civilians shall as far as possible be the same as that fixed for privates.. . .

Text from : http://www.yale.edu/lawweb/avalon/diplomacy/soviet/sov007.htm