The victims are two people killed by falling trees in Florida and Alabama, officials said, Xinhua reported.
Nearly 670,000 customers remained without power in Florida, Alabama, Georgia and Mississippi as of midday Saturday, data from utility tracker PowerOutage.us showed.
Isaias is forecast to continue weakening as it moves inland this weekend. But as hazardous conditions remain and storm surges, flash flooding, damaging winds and a risk of tornadoes across parts of the US Southeast are expected, the National Hurricane Center (NHC) said.
Recovery efforts have begun along the Gulf Coast as Isaias has spread damage across several states.
Businesses, roads and airports are reopening in areas impacted by the storm, but new flooding could still occur in the next couple of days, Florida officials said at a press conference Saturday afternoon. Downed trees and debris are still contributing to widespread power outages in the region.