Interflug did not fly to the US at all. All down to diplomacy but presumably there was little or no commercial demand either. They did operate to Havana, Cuba, using Shannon and/or Gander and/or Santa Maria, Azores, as refuelling stops, but kept well clear offshore from US airspace, the same as Cubana flights did (ironically US flights overfly Cuba all the time - apparently Havana Center now speaks better English than Miami does !) The Il-62M (the re-engined and updated one - Interflug had them) could indeed have attempted New York to Berlin - they did New York and Toronto to Warsaw for LOT for years. However Havana is a lot further and needs a fuel stop.

Interflug also did not fly to the Western Europe "allies" countries like Britain or France either, nor West Germany, although they did get to Netherlands and such like on regular flights. There were very occasional Interflug charter flights to the UK, with ships crews and similar, generally using the old Il-18 big turboprops.

Interflug did indeed attempt to compete as a commercial airline. That's what the A310s were for. They business was gone in months however !