Johannsson is awaiting completion of paperwork that would make him eligible to play for the U.S. The forward, who plays for AZ Alkmaar in the Netherlands, needs approval from FIFA to make the switch because he played for Iceland in eight qualifiers for the 2012 UEFA Under-21 Championship.
The 22-year-old was born in Mobile, Ala., but moved back to his parents' native Iceland when he was 3.
Most of the players called up for the three-day camp are based in Europe, though coach Jurgen Klinsmann did bring in Seattle's Brad Evans and Eddie Johnson. Mexico-based Edgar Castillo, Joe Corona and Michael Orozco Fiscal also were included on the roster. U.S. captain Clint Dempsey, who just completed a move from England's Tottenham Hotspur to Seattle, was not brought in.
The Americans, who have a record 11-game winning streak, play Bosnia-Herzegovina on Wednesday in Sarajevo. It is their only game before World Cup qualifying resumes Sept. 6 in Costa Rica.
"Our European-based players are just getting started with their seasons and this gives them a chance to get going a couple weeks before our big World Cup qualifiers," Klinsmann said. "We're also excited to bring some new faces into the senior team and have them start to become part of the group."
Goalkeepers: Cody Cropper (Southampton, England), Brad Guzan (Aston Villa, England), Tim Howard (Everton, England).
Defenders: John Anthony Brooks (Hertha Berlin, Germany), Geoff Cameron (Stoke City, England), Edgar Castillo (Tijuana, Mexico), Brad Evans (Seattle), Michael Orozco Fiscal (Puebla, Mexico), Michael Parkhurst (Augsburg, Germany), Tim Ream (Bolton, England).
Midfielders: Alejandro Bedoya (Nantes, France), Michael Bradley (Roma, Italy), Joe Corona (Tijuana, Mexico), Mix Diskerud (Rosenborg, Norway), Fabian Johnson (Hoffenheim, Germany), Jermaine Jones (Schalke, Germany), Sacha Kljestan (Anderlecht, Belgium), Danny Williams (Reading, England).
Forwards: Jozy Altidore (Sunderland, England), Terrence Boyd (Rapid Vienna, Austria), Eddie Johnson (Seattle), Aron Johannsson (AZ Alkmaar, Netherlands), Bobby Wood (1860 Munich, Germany).