The promotions formalise the existing situation - Clarke was previously the business director overseeing Starcom Motive's international department.
They also mark an attempt to improve the service levels the agency offers its international clients.
Clarke joined the agency nine years ago from McCann-Erickson New York, where he also worked on international business. He works with clients including UBS, Nintendo and McDonald's.
His counterpart Store joined the agency as a business director earlier this summer from the full-service digital agency Profero. Before joining Profero, Store spent five years working at Carat International.
"The network has reached a critical point of maturity that requires this increased investment behind our Fuelling Brand Power proposition," Mark Cranmer, the chief executive of Starcom Group, commented.
Separately, Will Saunders has been appointed the first client services director at Starcom Motive UK.
Saunders takes on responsibility for developing client services. He retains his responsibility for his existing accounts, including United Biscuits and Honda.