Israel said on Wednesday that Iran has used its Parchin military base as the site for secret tests of technology that could be used only for detonating a nuclear weapon.
The Jewish state has been a severe critic of six big powers' negotiations with Iran on restraining its nuclear program, suspecting Tehran is only trying to buy time to master sensitive nuclear know-how and would evade the terms of any final deal.
The Islamic Republic says allegations that it is seeking a nuclear weapons capability are false and baseless. Tehran says it is Israel's assumed atomic arsenal that is a destabilizing threat to the Middle East.
A statement from Intelligence Minister Yuval Steinitz, issued a day before Iranian President Hassan Rouhani - the architect of Tehran's diplomacy with the big powers - was to address the UN General Assembly, said internal neutron sources such as uranium were used in nuclear implosion tests at Parchin.
Israel, his statement said, based its information on "highly reliable information," without elaborating.