Iran, the United States and other major powers struggled yesterday to break a deadlock in nuclear talks that has held up a historic deal that would bring sanctions relief for Tehran in exchange for curbs on its atomic programme.

Tehran and the six powers have given themselves until tomorrow to reach a nuclear agreement, their third extension in two weeks, as the Iranian delegation accused the West of throwing up new stumbling blocks to a deal. Among the biggest sticking points at the moment is Iran's insistence that a United Nations Security Council arms embargo and ban on its ballistic missile programme dating from 2006 be lifted immediately if an agreement is reached.