Marathon talks aimed at stopping Iran from acquiring nuclear weapons entered their final scheduled day Tuesday with global powers racing to agree a framework deal by midnight deadline. An army of technical and sanctions experts worked until the small hours in Switzerland exchanging documents and trying to figure out how to put together what would be a highly complex agreement. US Secretary of State John Kerry, in Lausanne since Wednesday in the latest in a series of meetings around the world with Iranian counterpart Mohammed Javad Zarif, late Monday said there “still remain some difficult issues.” “We are working very hard to work those through. We are working late into the night and obviously into tomorrow (Tuesday),” Kerry told CNN. A meeting between Kerry and his counterparts from the other five powers began shortly after 7:00am and they were joined half an hour later by Zarif and other members of the Iranian nuclear team. Under the deal due to be finalised by June 30, the powers want Iran to scale back it’s nuclear program to give the world ample notice of any dash to make the bomb by extending the so-called “breakout” time. In return, the Islamic republic, which denies wanting atomic weapons, is demanding the lifting of sanctions that have strangled it’s economy.