Strikers Landon Donovan and Jozy Altidore and defender Oguchi Onyewu were among 11 players announced on Sunday by US Soccer as additions to the American training camp ahead of 2014 World Cup qualifiers.
US coach Jurgen Klinsmann welcomed Los Angeles Galaxy forward Donovan and four other Major League Soccer players plus Borussia Dortmund forward Terrence Boyd as Sunday arrivals at Orlando, Florida, for twice-a-day workout sessions.
Sporting Lisbon's Onyewu is set to arrive on Monday, a week ahead of AZ Alkmaar's Altidore, who figures to be in the final 23-man roster picked from 27 hopefuls for five upcoming matches that Klinsmann will select next Friday.
"We are excited now to get towards full numbers with the MLS guys and also the players from Europe who are coming in with great form," Klinsmann said.
"We want them to pick up the rhythm as fast as possible and make them understand that we are taking the next couple weeks very seriously."
Donovan is the all-time US scoring leader while Altidore scored 19 goals for AZ Alkmaar this season.
The Americans will play host to Scotland on May 26 at Jacksonville, Florida, and five-time World Cup champion Brazil on May 30 at Washington before a visit to Toronto for a friendly against Canada on June 3.
US players launch their quest for a seventh consecutive trip to the World Cup on June 8 when they entertain Antigua and Barbuda at Tampa, Florida, in their first semi-final round match of CONCACAF regional qualifying. Four days later the Americans visit Guatemala.