London Mayor Sadiq Khan is under fire once again for prioritizing a ban on junk food advertising for the city’s transportation network while citizens grapple with a spate of stabbings.

A flood of negative social-media feedback greeted Mr. Khan on Friday as he unveiled a “package of measures” aimed at curbing childhood obesity. The policy was touted as a “great example” by former New York City Mayor Michael Bloomberg, but panned in Mr. Khan’s Twitter feed.

“London has one of the highest childhood obesity rates in Europe, with 40% of children aged 10 & 11 overweight or obese,” Mr. Khan tweeted. “As part of a package of measures in our new London Food Strategy — we’re proposing to ban harmful junk food ads from the entire Transport for London network.”