Iran's foreign minister said Tuesday that bilateral discussions with the United States before a historic nuclear agreement were limited to the atomic issue and not rapprochement with Washington.

Mohammad Javad Zarif's remarks came after a senior US official said a series of secret meetings between Iranian and American envoys had taken place since the June election of President Hassan Rouhani in preparation for Sunday's nuclear deal.

"Our discussions have been limited to the nuclear issue," Zarif said in English when asked about the revelation, without directly commenting on them or giving any details.

"All the speculations about discussions involving other issues are flatly wrong, as we've only concentrated on the nuclear issue," he said.

Zarif led the Iranian team at the talks with the P5+1 group of world powers in Geneva, which culminated in the landmark agreement elusive for the past decade in freezing parts of Iran's nuclear activities in exchange for limited sanctions relief.

Iran and the United States broke diplomatic ties following the 1979 hostage taking of American diplomats in Tehran, and have weathered rising tensions in recent years over a number of issues.

Any decision on contacts with Washington, or eventual thaw in relations, rests in the hands of Iran's ultimate authority, supreme leader Ayatollah Ali Khamenei.

Zarif met face-to-face for an hour with his US counterpart John Kerry in New York in late September, the first such meeting since the 1979 Islamic revolution in Iran.

The two also spent several hours in bilateral sessions in the nuclear talks between Iran so-called P5+1 group of the United States, Britain, France, China and Russia plus Germany.

"In discussions on the sidelines of the P5+1 there were various countries, including the United States," Zarif said.

"We made it very clear that there is no problem for Iran to discuss with all the parties... on the resolution of the nuclear issue."

After the agreement was reached Sunday, a senior US official said contacts with Iran were established and series of meetings to "reinforce and ultimately to being part of the P5+1 negotiations."

Speaking not for attribution, the official was commenting on a detailed report on the specialist Middle East news website Al-Monitor which says the contacts had started before Rouhani's election.

Zarif did not directly comment on these reports.

In March, Khamenei -- who also has final call on Iran's nuclear activities -- hinted at green-lighting first direct contact with the US.

"US officials time after time have offered one-on-one talks," Khamenei said in televised address then. "I am not optimistic about these (direct) talks but I am not opposed to it either."

Iran's atomic chief Ali Akbar Salehi, who was foreign minister from late 2010 to August 2013, refused Sunday to comment on the backchannel contacts.

"Do I have to answer all questions?" he said in English, with a grin on his face, when asked if contacts had been established before Rouhani was elected.

Rapprochement with the United States is a sensitive issue in Iran, where any progress on this front is likely to rile hardliners and ultra-conservatives.

The interim agreement in Geneva is valid for six months to allow for more diplomacy before a final deal is clinched that would once and for all remove suspicions in the West that Iran's nuclear drive masks military objectives.

Iran -- which insists its activities are for peaceful nuclear purposes -- hopes the final deal could be agreed within a year, Zarif said.

"It is clear that our ultimate goal is to eliminate all UN sanctions as well as unilateral ones" imposed by the US and the European Union, said the foreign minister.

"According to the agreement, we have a year to conclude the negotiations but we want to be ambitious and aim for six months," he added.