A government statement Wednesday said Artur Neves resigned for personal reasons. However, the attorney general's office had announced earlier in the day that Neves' office was among dozens being searched in the operation.
The attorney general's statement said the investigation targets potential misuse of public funds to acquire emergency kits distributed among villages and hamlets at risk from Portugal's annual summer wildfire scourge.
The investigation comes at a bad time for the governing Socialist Party, with a general election less than three weeks away.
Recent opinion polls have indicated that the center-left Socialists have a strong lead before the Oct. 6 ballot.
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