Gulf diplomats and Iranian officials were set to meet Monday to discuss an Omani plan for reopening the Strait of Hormuz to regular tanker traffic, a conversation that would have happened without a critical player: the United States.

One source said details had yet to be finalized, but several countries had already confirmed their participation

TEHRAN — Iran's foreign ministry said the country would meet with Gulf states in Oman on Monday to discuss the strategic Strait of Hormuz, which th...