“Iran knows that they still have an open window to choose wisely at the negotiating table,” Mr. Hegseth told reporters at the Pentagon.

Many sticking points remain, including the reopening of the Strait of Hormuz; the fate of Iran’s highly enriched uranium; and Tehran’s demand that about $27 billion in frozen assets held abroad be released.

The United States and Iran agreed to a cease-fire more than two weeks ago. Still, tensions have remained high in and around the strait, a crucial conduit for Persian Gulf crude oil and natural gas. On Tuesday, Mr. Trump said he was extending the cease-fire indefinitely. But both Iran and the United States have continued to seize vessels they said have violated their restrictions on shipping in the waterway.

On Friday, the U.S. Treasury Department rolled out a blitz of new sanctions targeting 40 shipping firms and vessels it said were part of Iran’s “shadow fleet” of oil tankers. It also imposed sanctions on a China-based independent refinery, Hengli, which the Treasury identified as one of Iran’s largest customers for crude oil and other petroleum products.The United States and Iran moved to resume talks as clashes between Israel and Hezbollah, the Iranian-backed militia, intensified in Lebanon on Friday, straining a separate cease-fire that was also extended by the White House.

Mr. Trump announced a three-week extension of the truce in Lebanon on Thursday, after hosting Israeli and Lebanese diplomats at the White House. Hezbollah, which is not part of the negotiations, has signaled it intends to abide by the truce if Israel does the same.

Strikes between Israel and Hezbollah have plummeted since an initial cease-fire was announced last week. But both sides have continued to exchange fire, raising fears that the truce could collapse into an all-out war.

“Cease-fire? What cease-fire while drones are still hovering above us?” said Fatima al-Masri, 49, who was in the southern Lebanese town of Qana on Friday. She was visiting the grave of her husband, an emergency worker, who had been killed in the conflict.

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