Pentagon officials, surprised by President Trump’s orders, scrambled to work out a plan to halt sanctioned tankers as Nicolás Maduro, Venezuela’s leader, vowed resistance.

© Adriana Loureiro Fernandez for The New York Times

A firm controlled by a businessman tied to a seized tanker carrying Venezuelan oil has sold millions of barrels from a Chevron-operated oil field.

© Adriana Loureiro Fernandez for The New York Times

Firms with ties to Cuba are getting a larger share of Venezuelan oil exports, as the island’s security agents boost President Nicolás Maduro’s defenses.