The last-minute scuttling of the trip to Pakistan was the latest sign of how far apart the two sides are on reaching a deal to end the Iran war.

In an unsanctioned mission, the Foreign Service officer helped evacuate about 200 South Vietnamese citizens from Saigon days before the city fell in 1975.

President Trump withdrew from the Obama-era nuclear accord in 2018, saying it was the worst deal ever. But Iran responded with an enrichment spree that haunts the negotiations to this day.

President Trump has outsourced much of his diplomacy to others, while Mr. Rubio focuses on his second job as national security adviser.

Iran’s foreign minister has already arrived in the country, state media reported. He was believed to be carrying a written response to a U.S. proposal to end the war.