ATHENS, Greece—Rescuers searching through the rubble of a two-story house that collapsed after an explosion in Athens ’ historic Plaka district recovered six bodies on Saturday, authorities said.

Documents and belongings found with four of the victims—two men and two women—indicated they were U.S. citizens, according to Greek state broadcaster ERT and other local media reports.

The blast on Friday was believed to have been caused by a major gas leak, Athens Mayor Haris Doukas said. Neighboring buildings were damaged and evacuated, he added.

Plaka lies at the foot of the Acropolis, Greece’s most visited ancient monument.

Two women were injured in an adjacent building on Lysikratous Street, the fire department said. The search-and-rescue operation involved 30 firefighters and three dogs, and an investigation into the explosion was underway.

Video from the scene showed rubble strewn across the street and parked cars crushed by falling debris. Resident Andreas Martzaklis said all those rescued from the adjacent building were tourists.

The pastor of a nearby church said Sunday’s service would be held outdoors because the building had been damaged.