Iran was allowed to evade a number of restrictions specified in the nuclear agreement signed with a group of world powers last year, according to a new report.

In the report, seen by news agency Reuters, the Washington-based Institute for Science and International Security reveals it was told by several “knowledgeable” officials involved in the negotiations that Tehran was allowed to exceed the agreed-upon limits of how much low-enriched uranium could be kept at its nuclear facilities.

The science institute reportedly said that the P5+1 negotiating powers — the US, Britain, China, France, Germany and Russia — also let Tehran ship 50 tons of heavy water from its Arak plant to Oman, where it could be kept under Iranian supervision.

According to the report, the negotiating powers made the concessions in order to meet the deadline for Iran to start getting relief from economic sanctions.

The president of the institute, David Albright, who co-authored the report, said the “exemptions or loopholes are happening in secret, and it appears that they favour Iran”.