At the close, the Dow Jones Industrial Average gained 1.9 percent, the broad S&P 500 index rose 1.8 percent, and the technology-heavy Nasdaq Composite rose 2.5 percent.
The first few hours of trading were subdued. But then President Trump published a post on Truth Social announcing that planned attacks on Iran had been called off and that the parties were once again claiming to be close to ending the war.
Among the top gainers were several tech stocks, such as Micron, Intel, and Advanced Micro Devices.
The price of oil fell sharply after the move. At 10 p.m., a barrel of North Sea oil was under $89, compared with around $93 earlier on Thursday evening.
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