Fewer customers are visiting UK Starbucks outlets, the firm said.
Starbucks has seen its first quarterly net loss in more than 15 years - blaming costs linked to closing about 600 of its underperforming stores.
The Seattle-based firm lost $6.7m in the three months to 29 June, compared with a $158.3m profit a year earlier.
Starbucks also said it would close more stores than it would open next year.
It has been struggling in the US as consumers have cut back their spending on expensive coffee. Rising dairy prices have also raised costs.
There has also been increased competition with the likes of Dunkin' Donuts and McDonald's introducing their own lines of gourmet coffee.
Starbucks said that there had also been a fall-off in customers in the UK, while sales growth had slowed in Canada.
Earlier this week it said it planned to shut 61 of its 85 stores in Australia.
Starbucks, which has also announced plans to cut 1,000 office jobs, said sales rose 9% to $2.57bn.