TEHRAN — Wearing business suits set off with sneakers, the American executives trailed a young guide along the narrow sidewalks of the capital of Iran, once branded by the United States as part of the “Axis of Evil.”

Their destination was one of Tehran’s most luxurious restaurants, where Iranian officials and business consultants greeted the visitors with open arms and the Pharrell Williams song “Happy” blasted from the sound system.

“Everybody loves us here,” said Ned Lamont, a digital services entrepreneur and former politician, holding a glass of carrot juice offered by one of his hosts.

Just as the Obama administration and Congress were wrangling over details of a nuclear agreement with Iran last week, the group of 24 executives were touring the country on a fact-finding mission.