Iran’s foreign minister said on Monday some differences still remained between Iran and the six powers over the country’s disputed nuclear program ahead of Tuesday’s deadline for a final agreement to end a 12-year-old dispute. “Still nothing is clear. Some differences remain and we are trying and working hard,” Mohammad Javad Zarif told reporters. The deal under discussion between Iran and the powers is aimed at curbing Tehran’s most sensitive nuclear work for a decade or more in exchange for relief from sanctions that have crippled the country’s economy. US Secretary of State John Kerry said on Sunday that reaching an agreement is possible this week if Iran makes the “hard choices” necessary, but if not, the United States stands ready to walk away from the negotiations.