Australian full-back Marc Warren, 18, has completed a move from Central Coast Mariners, while the Blades have also moved to sign midfielder Andras Gardos, 20, from Hungarian sister club Ferencvaros. Kristoffer Lokberg and Erik Tonne, both 19, have also joined United, joining from Norwegian club Strindheim.
Coach Mark Smith, who will oversee the quartet's progress, told the club's official website: "We have identified that all four have potential and we hope that we can boost their development by working full-time at (the club's training base) Shirecliffe.
"The signing of these players emphasises our long-term thinking, but they are settling in to Yorkshire life nicely, working hard on the training pitch and, hopefully, they can catch the eye of Micky Adams in the future."
Club chief executive Trevor Birch added: "Whilst we have a job to do for the first team, there is a vision as to how the club should be run and the identification of youth talent to develop is a core element. Our extensive scouting has identified some of the best youth talent available."
Source: PA
Source: PA