A new report is raising concerns about some of the bolts used to build the Mario Cuomo Bridge. 

Officials from the New York state Attorney General's Office say they are investigating an alleged cover-up about the steel bolts.

According to published reports, a small number of the steel bolts used to hold the bridge's twin spans together broke apart during construction of the $3.9 billion bridge.

MORE: Report: Steel bolts used in building of Gov. Mario Cuomo Bridge broke during construction

The reports say up to 1 million of the bolts were used, and about 60 failed.

There are now questions about why the bolts failed and whether the contractor that built the bridge, Tappan Zee Constructors, tried to hide the problem from the state Thruway Authority.

Tappan Zee Constructors issued a statement saying it is cooperating with the investigation and, "To date, all bolt testing performed by multiple parties indicates there is not an issue with the bolts."

There are no immediate safety concerns.  The broken bolts were discovered in 2016, and testing was done by the Thruway Authority a year later.