"We reached a preliminary agreement at the experts level, which means a framework that contains the main viewpoints of both sides," top Iranian negotiator Husain Mussavian told state television on Sunday.
"This agreement is to be taken to the capitals of the four countries, and in the next days, if the capitals approve it, it will be announced officially," he said.
"Should the four countries be able to agree on a package in a not so distant future, there would be a crucial transformation in relations between Iran and the EU and the whole international community."
His announcement followed talks between Iran and Britain, France and Germany on getting Tehran to suspend uranium enrichment in order to avoid being hauled before the United Nations Security Council for possible sanctions.
The US accuses Iran of secretly trying to develop nuclear weapons under cover of its civilian atomic energy programme and wants the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), to refer Tehran to the Security Council when the agency meets in Vienna on 25 November.
Mussavian said the preliminary agreement included "a collection of political, economic, security, technological and trust-building cooperation regarding the future of Iran's peaceful nuclear activities".
But he refused to give any specific details pending its approval by "the most senior officials" in the country as well as in the capitals of the EU's so-called "big three".
Husain Mussavian is optimistic
the latest nuclear deal will stick
"I must emphasise that all this is pending the agreement of the four capitals. If it is not approved, we will have to say these discussions failed. But I am not pessimistic," he told state television.
He also made no mention of whether Iran had agreed to meet EU demands that it halt its controversial work on the sensitive nuclear fuel cycle, activities that officials there insist are only aimed at producing fuel for civilian reactors.
According to diplomatic sources, Europe's three powers are believed to have offered Iran nuclear technology, including access to nuclear fuel, increased trade and help with Tehran's regional security concerns in exchange for a halt to enrichment.