McDonald's Corp. (MCD) Monday said worldwide sales at hamburger restaurants open more than a year rose 6.4 percent in July, helped by strong gains in its U.S. business.

The world's largest fast-food chain said same-store sales, a key measure of retail strength, rose 7.8 percent in the United States, its largest market.

Same-sales rose 2.1 percent in Europe, the Oak Brook, Ill., company's No. 2 market.

Prudential analyst Larry Miller had been expecting U.S. same-store sales to rise between 6.5 percent and 7 percent, and forecast a 3 percent gain in Europe.

In a statement, McDonald's Chief Executive Charlie Bell (search) said the company expects sales in Europe to improve as it works on turning around its business in the United Kingdom and expanding its menu offerings.

"I have higher expectations for revitalizing the performance of this key business segment," Bell said.

McDonald's shares dipped 7 cents or 0.3 percent to $26.27 Monday on the New York Stock Exchange (search).