With their July 20 target date for a nuclear deal only weeks away, Iran and six world powers are meeting to see if stubborn differences can be overcome.

The negotiations that began Tuesday follow a stalemated May round. Senior U.S. and Iranian officials then met subsequently but two diplomats familiar with the discussions say they failed to resolve the disputes.

They say the main obstacle is the size and capacity of Iran’s future uranium enrichment program. Enrichment can create both nuclear fuel and the core of an atomic weapon.

The U.S. and its allies want strict limits on Iran’s enrichment capacity. Iran is resisting and insists it does not want nuclear arms.

The diplomats demanded anonymity because they are not authorized to discuss the confidential talks.

(AP)