TEHRAN, (Reuters) – Turkey said yesterday Iran had  agreed on a nuclear fuel swap deal which could help end Tehran’s  stand-off with the West over its atomic programme.

Full details of the agreement were not immediately released  by Turkish and Brazilian officials mediating in Iran’s dispute  with leading world powers, who suspect Tehran of covertly  developing a nuclear bomb.

Turkey’s foreign ministry said a formal announcement might  be made today after any final revisions by the Brazilian and  Iranian presidents and the Turkish prime minister.

“Yes, it has been reached after almost 18 hours of  negotiations,” Turkish Foreign Minister Ahmet Davutoglu told  reporters in Tehran when asked if there would be an agreement.

Earlier, Turkish Prime Minister Tayyip Erdogan flew to  Tehran to join Brazilian President Luiz Inacio Lula da Silva who  has been negotiating with Iranian officials in what Western and  Russian authorities have said is probably the last chance to  avoid new U.N. sanctions against Iran.

A U.N.-backed deal offered Iran last October to ship 1,200  kg (2,646 lb) of its low enriched uranium — enough for a single  bomb if purified to a high enough level — to Russia and France  to make into fuel for a Tehran research reactor.

Iran later said it would only swap its LEU for higher grade  material and only on its own soil, conditions other parties in  the deal said were unacceptable. It denies seeking to build an  atomic bomb.

“I am going to Iran because a clause will be added to the  proposal which says the swap will take place in Turkey,” Erdogan  had said earlier.

“We will have the opportunity to start the process regarding  the swap,” he said. “I guarantee that we will find the  opportunity to overcome these problems, god willing.”