The State Department is so worried that a Russian diplomatic compound in the Bronx is serving as a Russian spy hub that it held a classified briefing about the compound on Friday.

The previously unreported briefing touched on concerns about the compound and its potential ties to Russian espionage operations—concerns which Rep. Ritchie Torres (D-NY) raised in March of this year when he sent a letter to the Directors of the FBI, CIA, the Director of National Intelligence, and the Departments of Homeland Security and Justice.

It’s not clear what the outcome of the meeting was. Torres declined to comment on what was discussed in the meeting, citing the classified nature of the gathering. Due to security reasons, the State Department also declined to share details about the meeting.

But the compound—located at 355 West 255th St. in Riverdale, NY—has long been suspected to serve not only as a residence for Russian diplomats, but also as an outpost for Russian intelligence agencies. Ever since the austere, 20-story white building in the complex was constructed in the 1970s to serve as an enclave for Russian diplomats working at the United Nations (UN), it’s been the focus of speculation that the Russians are using the building’s towering perch to conduct surveillance, evade U.S. intelligence operatives, and conduct other spy work.

Many Russian spies have been linked to the complex over the years. Earlier this year the United States expelled 12 Russian diplomats from Moscow’s UN mission for conducting intelligence operations against the United States. The Russian mission said at the time that most of its diplomats lived in the building.

In 2015, the FBI arrested Evgeniy Buryakov, a Russian man who eventually pleaded guilty to working for Russia’s Foreign Intelligence Service (SVR), and who lived nearby the compound. He worked under non-official cover and appeared to have a regular job as a banker in Manhattan, but really traded coded messages with Russian spies that went straight back to Moscow, according to the Department of Justice.

In a classic case of spy versus spy, U.S. intelligence operatives have been working to track the Russian agents there for years. Robin Dreeke, a former FBI Special Agent and Head of the Counterintelligence Behavioral A***ysis Program, told The Daily Beast that he and fellow FBI agents tried to track and recruit Russian spies known to live at the compound.

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So classified that we are hearing of it 2 days later