North American potash inventories at the producer level, a key indicator of market sentiment, rose in May to well above-normal levels, according to Potash Corp.

Stockpiles of potassium chloride -- the key crop nutrient more commonly known as potash -- climbed last month to 3 million tonnes, up 3.9 percent from April.

Sluggish demand had led Potash Corp to slow production at some mines during the winter, before returning to full speed.

Potash inventories now stand 43 percent higher than the previous five-year average, according to data posted on Potash Corp's website on Thursday.

Spot potash prices hovered close to $500 per tonne.

The vast majority of the potash produced in North America is mined in the western Canadian province of Saskatchewan, where Potash Corp is headquartered. Minnesota-based Mosaic Co and Calgary, Alberta-based Agrium Inc are the other two large potash miners in the province.