McDonald's global sales at stores open at least 13 months declined 3.7% in August.

That the worst same-store sales decline that the fast-food giant has reported since March 2003, when global sales also fell 3.7%. It also marks the fourth straight month of comparable sales declines in the U.S., which accounts for about 32% of McDonald's revenue.

Same-store sales in the U.S. were down 2.8%, and in the Asia/Pacific, Middle East, and Africa region they dropped 14.5%.

"During August, McDonald's global business faced several headwinds that impacted sales performance," McDonald's President and Chief Executive Officer Don Thompson said in a statement. "We are diligently working to effectively navigate the current market conditions to regain momentum. For the long term, we remain focused on strengthening the key foundational elements of our service, operations and marketing to maximize the impact of our strategic growth priorities for our customers and our business."

The company cited weak performance in Russia and ongoing fallout from a health scandal that affected one of its food suppliers in China as key factors affecting its sales.

Domestic same-store sales dropped 3.2% in July and 3.5% in June.