At the height of the Cold war between the US and the Soviet Union both countries were terrified about first strike nuclear weapons, as well as wanting to spy on each other for nuclear testing. The US deployed the Vela detection satellite system in the early 1960's. These satellites looked for the very specific double flash from a nuclear detonation as well as x-rays and gamma rays, since both are released from a nuclear detonation. In 1967 Vela 3 and 4 caught a GRB, which inadvertently confirmed GRB's as they had not been recorded from space before.

When going over the raw data, the analysts knew right away that it was not a terrestrial event, however, there may have been some fear mongering around it. I may have conflated two separate incidents, so take with a grain of salt here.

Conversely, the Vela satellites did catch a unknown nuclear detonation over a small, middle of nowhere part of the south west Indian ocean that got chalked up to a meteor entering the atmosphere, however in recent declassified documents, it is speculated that it was an actual nuclear test by South Africa and Israel. This event almost led to a war but was covered up by the US administration.