Amazon's big push into physical stores is taking a small step back. Well, 87 small steps back to be precise.

The online retailer plans to shutter all 87 of its pop-up kiosks in malls and shopping centers in the US next month, The Wall Street Journal reported Wednesday.

"After much review, we came to the decision to discontinue our pop-up kiosk program," an spokeswoman told the Journal.

The closures show how Amazon is continuing to experiment with physical store formats and hasn't yet landed on the perfect fit. Many industry watchers expect the company to ramp up store openings once it finds a format that it feels works best. While Amazon is the world's biggest online seller, most retail sales still take place in stores -- a major reason Amazon is working on building its own stores.

For now, the company is developing a lot of different concepts. Amazon started opening these pop-up locations, which showed off the company's lineup of gadgets, about five years ago. Along with these smaller-format stores, Amazon has opened three 4-star stores, which focus on top-rated items on its website; 18 Amazon Books bookstores and 10 Amazon Go convenience stores.

The company also owns and operates 500 Whole Foods supermarkets, and is planning -- according to the Journal -- another grocery store line that will offer cheaper prices.

The spokeswoman confirmed to the Journal that Amazon plans to expand its 4-star and bookstore locations this year, saying they both offer greater selection than the pop-up format.