SAN FRANCISCO — A criminal trial alleging FedEx knowingly delivered illegal prescription drugs to dealers and addicts ended suddenly on Friday when prosecutors moved to dismiss all charges against the shipping giant.

US District Court Judge Charles Breyer in San Francisco granted the request in a two-page order that did not indicate why prosecutors had decided to drop the case. The trial began on Monday.

The US Attorney’s Office confirmed in a statement that it had asked Breyer to dismiss the indictment but also did not say why. The office would have no additional comment, spokesman Abraham Simmons said.

FedEx spokesman Patrick Fitzgerald said in a statement the company has always been innocent and the case should never have been brought.

‘‘The government should take a very hard look at how they made the tremendously poor decision to file these charges,’’ he said. ‘‘Many companies would not have had the courage or the resources to defend themselves against false charges.’’

The trial — nearly two years in the making — was unusual in part because of the government’s decision to bring drug charges against a package delivery company.

In the early 2000s, prosecutors claimed, FedEx began conspiring with two internet pharmacy organizations to ship powerful sleep aids, sedatives, painkillers, and other drugs to customers who had not been physically examined by a doctor.

The crux of the government’s case was that FedEx knew the drugs were illegal and headed for dealers and addicts, some of whom died, but delivered them anyway.

Fedex said it only shipped what it believed were legal drugs from licensed pharmacies.