June 6 (SeeNews) - Bulgarian state-owned gas transmission operator Bulgartransgaz signed on Thursday two contracts worth nearly 485 million levs ($269.6 million/248 million euro) with consortia led by U.S.-based construction consulting firm Hill International and Bulgarian construction group Glavbolgarstroy (GBS) to expand infrastructure as part of an initiative to build a gas corridor linking Greece and northern Europe, the caretaker government said.