Iran and six major powers were exploring possible compromises to break an impasse in nuclear negotiations on Sunday, but officials cautioned they were unable to move on several sticking points.

The news came as Israel said the details of a possible agreement emerging from talks in Lausanne, Switzerland were worse than it feared.

In a significant development in talks aimed at securing a preliminary nuclear deal, several officials told Reuters that Tehran had indicated a willingness to accept fewer than 6,000 nuclear centrifuges and to send most of its enriched uranium stockpiles for storage in Russia.

Western powers, on the other hand, were considering the idea of allowing Iran to conduct limited, closely-monitored enrichment work for medical purposes at an underground facility called Fordow, the officials added on condition of anonymity.

Iran had originally insisted on keeping in operation the nearly 10,000 centrifuges it currently uses, but said in November that Washington indicated it could accept around 6,000. Iranian officials say they had been pushing for 6,500-7,000.

Chinese Foreign Minister Wang Yi arrived in Lausanne on Sunday to join the ongoing talks in an effort to push forward the expected framework agreement.

US Secretary of State John Kerry canceled plans on Sunday to return to the United States for an event honoring his late Senate colleague Edward Kennedy in order to remain at the talks.

The six world powers negotiating with Iran are seeking at least a 10-year suspension of its most sensitive nuclear work.

Reuters - Xinhua - AP