VIENNA (AP) — U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif are locked in negotiation with just two days left before their latest deadline for a comprehensive nuclear pact.

Kerry and Zarif met for 1 ½ hours Sunday morning in Vienna before a short break. By early afternoon, they were in discussions again.

World powers and Iran are hoping to clinch a deal by Tuesday, setting a decade of restrictions on Iran's nuclear program and granting Iran significant relief from international sanctions. Top diplomats from five other negotiating countries are expected to start returning to Austria's capital later Sunday.

Talks are making progress. Diplomats Saturday reported tentative agreement on the speed and scope of sanctions relief. Outstanding issues include inspection guidelines and rules governing nuclear research and development.