US government drivers trusted with transporting nuclear weapons are sometimes getting drunk while on duty, a Department of Energy investigation showed Monday.

The drivers were involved in 16 alcohol-related incidents from 2007 to 2009, with one agent arrested by police three years ago and two others handcuffed and detained last year, the Energy Department's office of inspector general said in a report.

The Office of Secure Transportation (OST) oversees the shipment of nuclear weapons, weapon parts and special nuclear material, with a workforce of nearly 600 agents.

"Alcohol incidents such as these, as infrequent as they may be, indicate a potential vulnerability in OST's critical national security mission," the report said.

Although the government has taken steps to address drinking by agents or candidates in training, "concerns expressed by some OST managers and the number of alcohol-related incidents occurring over the last three years suggests that further action may be needed," it said.

Two of the 16 alcohol incidents took place when convoy trucks were in "safe harbor" status and the agents had checked into local hotels.

In 2007, an agent was arrested for public intoxication and in 2009, two agents were temporarily detained by police after an unspecified "incident at a local bar," the report said.

Under new rules designed by the government agency, agents are barred from drinking alcohol eight hours before reporting for duty and agent candidates are prohibited from "possessing kegs of beer or quantities of alcohol in excess of what is reasonable for personal use," said the report.

The inspector general's office launched the probe after hearing allegations of alcohol abuse within OST and of incidents at a training facility in Fort Chaffee, Arkansas.