The U.S. flag flies from the main building of the U.S. Embassy in Moscow. (Sergei Ilnitsky/Epa-Efe/Rex/Shutterstock)

A Russian citizen who worked for more than a decade at the U.S. Embassy in Moscow was terminated last summer after she was discovered having unusual secret contacts with Russian intelligence agents, according to documents and two people familiar with the case.

The woman had worked as a local investigator in the U.S. Secret Service office in the embassy since 2001, the people said. But she was fired in early August 2017 after State Department investigators surveilled her movements and were alarmed to find her meeting and communicating with agents of the Federal Security Service, better known as the FSB, the people said.

It is unclear whether her FSB conversations led to any damage to national security. A Secret Service spokeswoman confirmed in a statement that the investigator lost her position after a standard security review. The statement stressed she would have “never been provided or placed in a position to obtain secret or classified information.”

The Secret Service issued a statement saying it conducted an internal review the day the State Department notified the service in July 2017 about proposing to terminate the Russian employee.

“The review resulted in the determination that no unusual activity occurred and there were no issues from a data exfiltration perspective,” the statement said.

But others with knowledge of her termination said the Secret Service failed to conduct a full damage assessment of the kind of information she may have accessed and shared over her 16 years in the office.

The Russian woman did have access to the Secret Service’s official email system, according to one of the people familiar with the termination. On this system, agents share closely held, but unclassified, information on plans for the president’s trips and schedule.

In her job, she served as a liaison between Russian law enforcement and the Secret Service, and former embassy staffers said she would have had access to information about agency investigations of financial fraud and cybercrimes. Secret Service investigators were the first to identify the Russian government as directing the 2014 hack into the White House’s unclassified email system.

The Washington Post, which was unable to reach the woman by email, is not identifying her by name.

A routine State Department security review first raised a flag about her FSB communications in 2016, and two State Department investigators began investigating and then reported their findings in the summer of 2017 to the embassy’s top security officer, Michael Mack, internal correspondence shows. She was stripped of her security access and barred from the building pending a full review. On Aug. 3, 2017, Mack formally recommended she be terminated, the records show. The ambassador at the time, John F. Tefft, later agreed.

Just after she was fired, the Secret Service closed down its small Moscow office, which normally was staffed by one resident agent. The timing of both the firing and the office’s closure coincided with a major blow to the embassy: President Vladi­mir Putin announced he was expelling hundreds of embassy employees from Russia.

The State Department declined to detail the reasons for the woman’s departure. Spokesmen for the State Department and the Secret Service emphasized that they are on guard for the risk of foreign service nationals being pressured to spy for their country.

“The U.S. Secret Service recognizes that all Foreign Service Nationals (FSN) who provide services in furtherance of our mission, administrative or otherwise, can be subjected to foreign intelligence influence,” a statement read. “As such, all Foreign Service Nationals are managed accordingly to ensure that Secret Service and United States Government interests are protected at all times.”

The State Department carefully vets and monitors foreign service nationals for this kind of security breach, a spokesman said.

“Diplomatic Security and other law enforcement agencies rigorously vet new hires at our missions overseas, and all employees are also subject to ongoing reviews to ensure they are fully complying with their security responsibilities and Department security requirements,” said a statement from the State Department. “When we identify an employee in violation of security directives, we take appropriate action at the appropriate time.”

The woman’s termination was first reported by the Guardian.

The woman was described by former co-workers as a native of St. Petersburg, a wife and mother, and a mild-mannered investigator who kept to herself. Her State Department employee picture shows a trim woman with a pale complexion and straight brown hair.

“She was not a social butterfly,” said David Rubincam, an FBI agent who served as the FBI’s legal attache in the U.S. Embassy in Moscow and retired in 2013. “There were a lot of Russians you would meet in the cafeteria. She wasn’t one of them. Pretty much kept to herself. Did her work and went home.”

U.S. embassies employ hundreds of local citizens to serve in a range of roles, including cafeteria workers and housekeeping staff as well as investigators and translators. In Russia, China and other adversarial countries, Rubincam said, U.S. officials assume foreign service nationals will be approached by their home country’s intelligence agencies for information.

In Russia, sometimes they will be pressured to begin working secretly for the FSB — to find out information the bureau is seeking about American diplomats or activities in the office.

“If you are a foreign-service-national investigator especially, the odds of the host nation, your own country’s intelligence agency, trying to sweet talk or strong-arm you for information is virtually 100 percent,” Rubincam said. “But you have to report it. If someone asks you to spy on the embassy that employs you, you have to report it. If you fail to report it, you’re gone.”

Rubincam said the FSB’s pressure on foreign nationals grew “increasingly aggressive” after Putin returned to the presidency in 2012. Some local employees found FSB agents in their apartments waiting for them after work.

“They pushed the door in on them when they got home from grocery shopping,” Rubincam said. “They said, ‘You’re going to do this, and you’re doing to do that.’ They tried to use leverage on them.”

To protect sensitive information, the U.S. Embassy in Moscow has created a “hard line” in the building, which means there are separate floors of offices where foreign service nationals are unable to go. U.S. Marines guard the entrance to their floors to check badges. People with blue badges — American staffers — can enter. Those with yellow badges — foreign nationals — cannot.

Julie Tate contributed to this report.