Defender Jonathan Spector has extended his stay at Birmingham after penning a new two-year deal.
Bastian Schweinsteiger’s Bayern Munich future remains in doubt after Matthias Sammer admitted he could leave the club.
Right-back Jonathan Rivierez, fellow defender Jose Luis Palomino and striker Juan Manuel Falcon have joined the Ligue 2 champions from Le Havre, Argentinos Juniors and Zamora respectively.
Rivierez will join his new team-mates in making the step up from the second tier while Argentinian Palomino is coming off a successful season in his homeland with San Lorenzo, who won the Torneo Inicial - the first half of the Primera Division season.
Club president Bernard Serin said: "We already have a good player on the right side of the defence with Romain Metanire but Jonathan Rivierez will strengthen us in that part of the field. He has a remarkable physical presence.
"(Palomino) is a powerful, left-footed player who was wanted by Benfica in Portugal two years ago."
Falcon, who is uncapped by Venezuela but has been a member of the Vinotinto squad, has scored 38 goals in the last two seasons in his home country and has experience of the Copa Libertadores, South America's main continental competition.
"We have signed a bird of prey," Serin joked. "Juan Manuel Falcon is a very athletic player with good firepower."
Both Falcon and Rivierez arrive on three-year contracts while Palomino has signed for two years.
The club also announced on Friday that midfielder Yeni Ngbakoto has signed a two-year contract extension to 2017.
The 22-year-old has broken through with 29 goals in the last two seasons in Ligue 2, having been with the club since 2006.