Department stores posted the largest year-on-year drop in sales in more than three years in July, as unfavorable weather conditions kept customers away and clothing sales slumped, an industry body said Tuesday.

Department store sales in the reporting month fell 6.1 percent from a year earlier on a same-store basis, the biggest decline since March 2015, when sales plunged 19.7 percent.

Torrential rain in western Japan followed by scorching heat throughout the nation dented the number of customer visits to stores 3.9 percent in the month.

Clothing sales dropped 11.1 percent after many stores brought forward clearance sales, the association said.

"The severe heat prevented the elderly, our main customers, from going out," an association official said.

Sales at all 219 stores run by 79 companies totaled ¥513.2 billion, while spending by inbound tourists rose 19.8 percent to ¥27.2 billion, marking the 20th consecutive month of increases, the association said.

The Japan Chain Stores Association said the same day that supermarket sales in July rose 1.5 percent from a year earlier on a same-store basis, the second straight month of rises, lifted by higher sales of agricultural products whose prices rose due to the extreme heat.

Sales at all 10,219 supermarkets run by 56 companies totaled ¥1.13 trillion in the month, the association said.