I'm betting that we're talking Civ 2, because Spies could indeed plant nukes. Also, the eco terrorism could be the guerillas generated when capturing a city or the massive barbarian swarms late in the game. Either Civ 2 or a mod making Civ3 more like Civ 2.
It's impossible to make a unit like that, and no espionage does not work that way, I've seen what you can do and the odds of succeding in anything you tell your spy to do.