A possible design flaw could be to blame for the bridge collapse that left five people dead in the United States one week ago.
National Transportation Safety Board investigators said they had found a potential design problem with gusset plates, or steel plates that tie together angled steel beams of the bridge's frame.
Investigators are trying to verify loads and stresses on these plates at specific locations as well as the materials used to construct them.
Officials stressed the finding is preliminary and would not say exactly where the plates were located or whether failure would have caused the collapse.
Meanwhile, navy divers are continuing to cut through tangled debris at the site of the collapse in Minneapolis in the search for victims.
Eight other probable victims are listed as missing.
The rush-hour collapse of the Interstate 35W bridge on 1 August hurled vehicles into the Mississippi River 20 metres below.
In the aftermath, officials demanded inspections of potentially suspect bridges across the United States amid renewed calls to improve the country's aging infrastructure.
