Iran has said evidence and documents offered by the US to the UN nuclear watchdog against Tehran's nuclear program are not authentic.

"All evidence given by the United States against Iran's nuclear program is fabricated," Iran's envoy to the International Atomic Energy Agency (IAEA) Ali-Asghar Soltaniyeh told reporters in Vienna after the agency briefed its 35 members on Thursday.

The envoy's comments followed accusations by the United States and its allies that Iran was developing a military version of its nuclear program.

The Iranian ambassador called on the UN nuclear agency to preserve its impartiality and not to turn a blind eye on Iran's good cooperation.

"It is high time that the member states should have a complete picture in order to have a better judgment because… the board of governors has put pressure on the secretariat to give impartial, incomplete reports and has created for the past five years many misunderstandings," said Soltaniyeh.

During the meeting Washington used its influence to focus on what it calls Iran's lack of cooperation, while ignoring the constructive work between the Islamic Republic and the IAEA.

"As today's briefing showed us there were strong reasons to suspect that Iran was working covertly and deceitfully at least until recently to build a bomb," US permanent envoy to IAEA Gregory Schulte claimed.

"Iran is refused to explain and even acknowledge past work of weaponization. This is particularly troubling when combined with Iran's determined effort to master the technology to enrich uranium," Schulte alleged.

Soltaniyeh slammed the accusations as baseless and fabricated, saying that none of documents presented by the United States had any seal or stamp of confidentiality.

"How can you have some sort of the Manhattan Project of nuclear weapons and all these communications of the (Iranian) Ministry of Defense that the Americans have none of them, have a seal of confidentiality," the Iranian ambassador argued.

In a sign of good will Thursday, Iran said it presented another document on the so-called 'Green Salt Project' which the United States presented as key piece of evidence on its anti-Iran campaign.

Soltaniyeh emphasized that the document was widely approved by the 35 board members as authentic and proving the veracity of Iran's statements.

The 35-member IAEA board is set to discuss the IAEA's May 26 report on Iran at its upcoming meeting on June 2-6.

Iran is a signatory to the Nuclear Non-Proliferation Treaty (NPT) and has all its nuclear activities under constant international supervision of the UN nuclear agency.