(ABC News)

Investigators are ruling as "accidental" the fire that destroyed a major section of Jersey Shore boardwalk last week, two officials briefed on the probe told ABC News tonight.

"It was not manmade," one of the of sources said of Thursday's fire in Seaside Park and Seaside Heights, N.J., without detailing what investigators found.

The other source elaborated, saying the blaze was electrical.

The findings are expected to be laid out in a news conference Tuesday.

The fire destroyed a length of boardwalk that was home to approximately 30 businesses, officials said.

More: Christie Vows to Get NJ Boardwalk Back to Normal After Fire

More: Residents Devastated by NJ Boardwalk Fire: 'Sandy Was Enough For Us'

The fire was another blow to a stretch of the Jersey Shore previously slammed by Superstorm Sandy in October 2012. Work crews had only completed repairs to the boardwalk destroyed by storm waters just before Memorial Day and in time for a visit from Prince Harry in May.

ABC News' Gio Benitez and Alexis Shaw contributed to this report.