U.S. intelligence has assigned more than 1,000 spies from 17 agencies to protect the Rio Summer Games and American athletes and staff as part of a highly classified effort, NBC News has learned.

Hundreds of analysts, law enforcement and special operations personnel are already on the ground in Rio, according to an exclusive NBC News review of a highly classified report on U.S. intelligence efforts.

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 on Olympic Security, according to senior military officials.

The U.S. military has also placed larger military units on call should a rescue or counterterrorism operation be needed, the officials said.

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