The co-creator of the Xbox has resigned days after Microsoft conceded the unit was struggling internationally and would miss its initial sales targets.

Seamus Blackley, a physicist by training who also worked in Hollywood before joining Microsoft (MSFT), plans to start a new venture, the details of which he will begin discussing in the next few weeks, said his spokeswoman, Susan Lusty.

News of Blackley's departure comes just days after Microsoft said it would miss its fiscal year-end sales target for the Xbox by as much as 40 percent, a shortfall it blamed on weak international sales. Those weak sales led to price cuts in Europe and Australia last week.

The console has also struggled in Japan, selling just over 190,000 units in its first six weeks there, according to Japanese game magazine publisher Enterbrain. By comparison, the console sold nearly 1.5 million units in its first six weeks in the United States last year.