Gap saw group sales fall by 8% to $1.09 billion (£557 million) in May but like-for-like sales were flat at its international division, which includes the UK.
In the US, Gap recorded more declines with Gap North America down 7% like for like and Banana Republic North America down 5% like for like. Old Navy North America recorded the worst performance with sales down 25% against the previous May.
Gap chief financial officer, Sabrina Simmons, said: "We were pleased that merchandise margins in May were significantly above last year. However, Old Navy continues to be our biggest challenge. As we have stated, we are working to rebalance Old Navy's mix of fashion and seasonal basic items, and expect to see improvements in the assortments by late fall."
Year-to-date net sales were down 6% to $4.47bn (£2.28m) for the 17 weeks to June 2. Year to date like-for-like sales were down 12%.