United States and Iranian negotiators headed to a Swiss venue Saturday for talks on adding key details to their interim agreement to halt the war, hours after Tehran said it closed the Strait of Hormuz because of Israel's attacks in Lebanon and warned that little might be achieved if the fighting doesn't stop.

US President Donald Trump, in response, unleashed a new threat to impose American tolls in the crucial waterway if a final deal with Iran isn't reached in 60 days, saying the money would be for "services rendered as the Guardian Angel to the countries of the Middle East". The agreement calls for toll-free travel for 60 days.

The announcements indicated a rough start to the technical-level talks that key mediator Pakistan said will begin Sunday, with Qatari mediators also participating.