The Justice Department said on Thursday that it has made “substantial progress” in finalizing an agreement with Boeing to plead guilty to defrauding the US government, but more time is needed to work out the remaining details.

After two jetliner crashes killed 346 people, a $2.5 billion settlement that let Boeing avoid criminal prosecution failed to resolve questions about the safety of the aerospace giant's planes.Federal prosecutors now accuse the company of failing to live up to terms of the 2021 settlement.

The U.S. Justice Department said on Thursday the government has made "substantial progress" toward reaching a final plea agreement with Boeing but does not expect to file the details before July 24.