Japan's consumer prices continued their long stretch of declines in May, falling for the 15th straight month, providing a reality check to any suggestion that an end to the nation's deflationary problem is just around the corner.

Further stoking concerns that entrenched price falls could choke off the country's economic recovery, the core consumer price index, which excludes volatile fresh food prices, dropped 1.2% from a year earlier in May, compared with a 1.5% fall in April, data from the Ministry of Internal Affairs and...