New Delhi, Dec. 18 -- President Donald Trump demanded Wednesday that Venezuela return assets that it seized from U.S. oil companies years ago, justifying anew his announcement of a "blockade" against oil tankers traveling to or from the South American country that face American sanctions.

Trump cited the lost U.S. investments in Venezuela when asked about his newest tactic in a pressure campaign against leader Nicolas Maduro, suggesting his administration's moves are at least somewhat motivated by disputes over oil investments, along with accusations of drug trafficking. Some sanctioned tankers already are diverting away from Venezuela.

"We're not going to be letting anybody going through who shouldn't be going through," Trump told repo...