Two Chinese diplomats were quietly expelled from the US after breaching a military base in September, according to a new report.

The New York Times said the incident appeared to be the first such expulsion in more than 30 years.

Chinese officials have been trying to access government facilities more often recently in an apparent effort to increase espionage activities.

The US government quietly expelled two Chinese diplomats suspected of spying after they drove onto a sensitive military base in Virginia, The New York Times reported Sunday.

The Times said the incident, which happened in September, appeared to be the first time Chinese diplomats had been suspected of espionage on US soil in more than 30 years.

It came after a pair of officials drove to the checkpoint for entry to a Virginia military base with their wives in September. A guard, who realized they did not have permission to enter, told them to go through the gate, turn around, and exit. But the officials instead continued to the base, those familiar with the incident told The Times.

Eventually, a fire truck was used to block their path. The Chinese officials said they had not understood the guard’s English instructions and had simply become lost, a claim officials were skeptical about.

At least one of the officials is believed to be an intelligence officer, six people with knowledge of the expulsions told The Times.

The incident, which was not announced by Washington or Beijing, underlines concerns within the Trump administration that Chinese officials have stepped up spying efforts amid an intensifying economic rivalry between the two countries.

Chinese officials carrying diplomatic passports have started showing up at government research facilities with increasing frequency in recent years, The Times reported.

The base Chinese officials tried to access in September was a sensitive unit housing special-operations forces and is near the US Navy base in Norfolk, Virginia.

The US is most recently known to have expelled Chinese diplomats on suspicion of espionage in 1987.