The aircraft will be operated by the group's new subsidiary in Argentina, Avian Lineas Aereas, branded as Avianca Argentina, ATR said in a statement.
Synergy Aerospace also placed options for a further six aircraft, it added.
ATR is a joint venture between Airbus Group (>> Airbus Group) and Italian aerospace company Leonardo (>> Leonardo Finmeccanica SpA). It competes for turboprop sales with Canada's Bombardier (>> Bombardier, Inc.).
On Monday, the Synergy group, which controls Latin American airline Avianca, announced a separate order for eight ATR turboprop planes as it disclosed plans to invest up to $100 million for a 49 percent stake in Mexican airline Aeromar.
(Reporting by Tim Hepher; editing by Laurence Frost)