After about five minutes of trading, the Dow Jones Industrial Average rose 0.9 percent, the broad S&P 500 index rose 0.7 percent and the tech-heavy Nasdaq Composite Index rose 0.8 percent.
After the stock market closed on Tuesday evening, Trump announced that the ceasefire with Iran would be extended, but that the blockade of Iranian ports would continue.
Oil prices were little changed on Wednesday. A barrel of North Sea oil cost $100.20 after rising 1.7 percent during the day.
