New Delhi, June 18 -- President Donald Trump signed an agreement with Iran on Wednesday that calls for Tehran to dilute its stockpile of highly enriched uranium and waives U.S.-backed sanctions on the country, immediately allowing Iran to sell its oil freely in a major concession from Washington, according to details released by both countries.

The initial deal to end the war takes "immediate effect" after leaders from both countries signed it, Pakistani Prime Minister Shehbaz Sharif, who helped mediate the agreement, said online.

The agreement calls for a permanent end to hostilities and starts a 60-day negotiating clock to reach a final deal on the future of Iran's nuclear program, though Trump left the door open to resume attacks. It...