NEW YORK - In its latest push to establish itself as a purveyor of premium burgers, Wendy's is testing a pretzel bun.

The Ohio-based chain has started selling a bacon cheeseburger in select locations made with a slightly heartier, pretzel-like bun.

A spokesman for Wendy's declined to confirm the tests or provide any details, such as the price or where exactly it's being offered. But the burger was spotted at a Wendy's in Miami and others have posted pictures on the social media site Twitter.

Wendy's executives have already said they plan to use better breads as a relatively low-cost way to raise perceptions about food quality.

The reliance on bread comes amid rising costs for beef, which have pressured restaurant chains struggling to keep prices down to hold onto price-conscious diners.