US President Donald Trump said that a US naval blockade against Iran could last months, leading oil prices Wednesday to spike to their highest in more than four years.

With diplomacy between Iran and the United States at a standstill after false starts, Trump spoke by phone with Russian President Vladimir Putin, who warned him of “damaging consequences” if the United States and Israel resume their war on Iran.

Meeting oil executives, Trump contended that the blockade of Iranian ports – which...