The freak elevator accident last month that killed a rising advertising executive inside a Midtown building was caused by maintenance work, The Post has learned.

Inspectors with the city’s Buildings Department have determined that repairs done by contractor Transel Elevator were likely a factor in the Dec. 14 tragedy that claimed the life of Suzanne Hart, agency spokesman Tony Sclafani said today.

Hart, 41, was crushed to death by an elevator inside 285 Madison Ave., a 25-story high-rise owned by global advertising giant WPP.

Since the accident, DOB inspectors undertook the biggest elevator sweep in history and examined 650 elevators citywide. Various violations were issued, but Hart’s death was a singular event, Sclafani added.