GENEVA (AP) — U.S. Secretary of State John Kerry and other top diplomats are heading into a tough round of negotiations in Geneva where six world powers are trying to reach a deal with Iran over its nuclear program. Kerry and the others joined the talks today on a first-step agreement that would begin to roll back Iran's nuclear program in exchange for the easing of U.S. and international sanctions that are hurting Iran's economy. The latest round of talks began on Wednesday, but so far there is no deal. Before he left Washington, Kerry said he had no particular expectation that an agreement could be reached this week. But after talking with top European Union diplomat Catherine Ashton on Friday, he decided to travel to Geneva to help negotiators narrow their differences.