August 7 (Reuters) - Supermarket group Ahold Delhaize beat second-quarter core profit margin expectations on Wednesday, supported by solid performances in its U.S. and European markets and cost control.

The group, which operates the Stop & Shop, Giant, Food Lion and Hannaford chains in the U.S. and the Albert Heijn and Delhaize chains in the Netherlands and Belgium, reported an underlying operating margin of 4.2% for the April-June period, topping the 3.9% expected by analysts polled by the company.

The company also reiterated its guidance for the year.

(Reporting by Stéphanie Hamel and Charlotte Bawol; editing by Jason Neely)