In an interview with the Financial Times, Trump says that just as the United States has supported Ukraine in the war against Russia, he expects Europe to help in the Strait of Hormuz.
"If there is no response or if there is a bad response, I think it will be very bad for the future of NATO," he tells the newspaper.
Since the outbreak of war just over two weeks ago, Iran has attacked and threatened shipping traffic in the Strait of Hormuz - through which approximately a fifth of the world's oil production passes.
Trump says he has asked about seven countries that depend on Middle Eastern oil to help guard the Strait of Hormuz, but he won't say who they are. He has previously urged China, France, Japan, South Korea and the UK to send ships to the Strait of Hormuz, but so far interest from those countries has been lukewarm.
"It is appropriate that people who benefit from the strait will help ensure that nothing bad happens there," Trump said.
The president also warns that a planned meeting with Chinese leader Xi Jinping later in March may be delayed if the country does not help reopen the Strait of Hormuz.
