As part of a highly classified operation to protect the Summer Olympics, U.S. intelligence agencies have assigned more than 1,000 spies to Rio, NBC News reports.

“Hundreds of analysts, law enforcement and special operations personnel are already on the ground in Rio de Janeiro, according to an exclusive NBC News review of a highly classified report on U.S. intelligence efforts,” the story reports. “In addition, more than a dozen highly trained Navy and Marine Corps commandos from the U.S. Special Operations Command are in Brazil, working with the Brazilian Federal Police and the Brazilian Navy, according to senior military officials.”

The officials noted that larger U.S. military units remain on call if needed for rescue or counterterrorism efforts.

“The classified report outlines an operation that encompasses all 17 U.S. intelligence agencies, including those of the armed services, and involves human intelligence, spy satellites, electronic eavesdropping, and cyber and social media monitoring,” NBC News notes.