Maduro says the economic crisis is due to a US-backed capitalist conspiracy.

Well, I don't think he's completely wrong when he says that. An empire needs to be in control of the sources of energy. If it isn't in control it automatically ceases to be an empire.

But Maduro says the opposition is conspiring with foreign entities, specifically the US, to destabilise the country.

It wouldn't be the first time. In fact, that is exactly what the CIA did in the Ukraine, in Syria, in Libya - just to name the more recent ones. But if you have a closer look you'll find out that they have been doing this at least since the 1950's. It is not unlikely that they would do the same in Venezuela. It is an oil rich country after all, and if you have oil you have two choices:

Either you hand it over to the price the empire dictates, or the empire will come and take it. That's geopolitics...