New Delhi, June 16 -- The United States and Iran reached an initial agreement early Monday to open the Strait of Hormuz and further extend a shaky ceasefire in the Iran war, potentially allowing desperately needed oil and natural gas to reach the global market.

Details of the deal were not immediately released and Iran signaled implementation would not start until the signing, which key mediator Pakistan said would occur Friday in Switzerland. It could provide a way to end a war that killed thousands across the Middle East, including the top leaders of Iran's theocracy, and sparked a historic energy crisis.

But the memorandum of understanding over the war already faced intense challenges. Israel's continued hostilities with the Iranian-...