Iran's senior envoys left talks in Switzerland on Monday after a marathon negotiating session with the United States, state media reported, as mediators claimed progress towards a definitive US-Iran deal.The host nation said conditions were set for technical talks to immediately follow, with the sides at the beginning of a 60-day period to secure a long-term settlement.Last week, Tehran and Washington signed a memorandum of understanding laying the groundwork for the negotiations, after a 40-day war that was followed by weeks of an inconclusive and oft-breached ceasefire.The negotiators aim to tackle some of the most intractable issues that have dogged US-Iranian relations for decades, including Tehran's nuclear programme and enriched uranium.Foreign Ministry spokesman Esmaeil Baqaei said on Monday that "a very brief discussion took place regarding the nuclear issue, but there was no discussion of details" and that nuclear talks had not begun.All the while, the war in Lebanon between Israel and Iran's close ally Hezbollah has threatened to collapse the ceasefire, though the country has been relatively calm since Sunday.Israeli leaders have expressed deep misgivings over the deal signed last week and have insisted that their troops will continue to occupy southern Lebanon and are free to respond to any threats there.Tehran and Washington, meanwhile, have set up communication lines to end the fighting in Lebanon and to keep the vital Strait of Hormuz open, mediators said, after the first round of talks.Iran closed the strait, through which much of the world's oil and gas travels in peacetime, early in the war, sending economic shockwaves across the globe.Before the conflict began, there was free international passage through the strait, but Tehran appears keen to monetise the waterway as part of any deal. It is also set to get some form of sanctions relief from Washington, with some assets unfrozen.- 'Roadmap' -Mediators Pakistan and Qatar said the negotiators reached agreement on a "roadmap towards reaching a final deal within 60 days", with technical talks to continue for the rest of the week at the Swiss resort of Burgenstock.