A US defence department linguist has been charged with transmitting "highly sensitive classified" information to a foreign national linked to the Lebanese Islamist militant group Hezbollah.
Mariam Thompson, 61, is accused of endangering the lives of US military personnel and others on "active" duty by revealing their real names.
Her alleged actions were a "threat to national security", US officials said.
Ms Thompson was arrested by FBI agents at an overseas US base on 27 February.
Formerly of Rochester, Minnesota, she worked as a contract linguist and held a "top secret government security clearance", the US justice department said in a statement on Wednesday.
"While in a war zone, the defendant allegedly gave sensitive national defence information, including the names of individuals helping the United States, to a Lebanese national located overseas," the justice department's assistant attorney general for national security, John Demers, said.
"If true, this conduct is a disgrace, especially for someone serving as a contractor with the United States military. This betrayal of country and colleagues will be punished," he added.
The statement says that an investigation into Ms Thompson established "a notable shift" in her network activity on the department's classified systems, including accessing "information she had no reason to access".
Then, on 19 February, an authorised search of her living quarters led to the discovery of a handwritten note in Arabic hidden under her mattress.
The note contained information "identifying human assets by name", while warning a person of interest affiliated with Hezbollah that these individuals' phones "should be monitored", the statement adds.
Ms Thompson allegedly shared the classified information with a "co-conspirator in whom she had a romantic interest". The FBI investigation revealed that she knew this person was a foreign national whose relative worked for the Lebanese government.
Ms Thompson is due to make an initial court appearance on Wednesday.
If she is later convicted, she faces a maximum sentence of life in prison.