"I don’t want to drive the oil prices up to $100 — $150, which could happen very easily. It is a very fragile market, I know it very well," Trump told reporters.
The United States granted waivers to eight nations — China, Greece, India, Italy, Japan, Turkey, South Korea and Taiwan — to purchase oil from Iran.
Trump characterized the issuing of waivers as the "absolutely right decision" and noted that his stance brought the oil prices down.
The US president said he is putting efforts to reduce the price of oil because he considers it to be a tax on consumers.
In May, Trump announced that the United States would withdraw from the Iran nuclear agreement and re-impose sanctions against Tehran that had been lifted under the accord.
The first round of the US restrictions entered into force in August, and a second, more severe round came into effect on Monday.