On the other hand, Russia was rumored to have been secretly buying Iranian oil previously and then reselling it as their own to European countries. Why couldn't they do it all over again?
After all, the US has no access to the Caspian Sea to check that trade (unlike the Persian Gulf)
This is the first time I am hearing about it. How can Iran smuggle oil to Russia, when dozens of American military satellites are scanning every square inch of the Russo-Iranian border? Also, I don't think that Russia will take
the risk of dishonoring the UN sanctionsIf I'm not mistaken there are no such sanctions
Provided you don't consider the US economic sanctions and oil embargo (as well as the EU's) as the same that UN imposes (the UN sanctions mostly prohibit selling of weapons to Iran). So there is no such issue as Iran smuggling oil to Russia since the latter could just buy the Iranian oil as it liked and then resell to whoever might want to buy it. These rumors are basically based on the increase in the official oil production of Russia which shouldn't have been there (and expected decrease after these sanctions had been lifted)