The United Nations nuclear agency said Monday that Iran’s role in a nuclear probe met all of the agency’s standards, after it had reportedly obtained environmental samples from Iranian experts as part of an ongoing investigation. Officials from the International Atomic Energy Agency (IAEA) said that they had made “significant progress” in the long-stalled probe into allegations that Tehran sought to develop nuclear weapons in the past, according to IAEA chief Yukiya Amano, cited by Agence France-Presse.

Amano added, however, that “much work remains” if the investigation is to be completed before the Dec. 15 deadline.

Under a major deal between Iran and the six world powers brokered in July, the country is required to significantly scale down its nuclear program -- which it insists it only operates for peaceful purposes -- and allow IAEA investigators to inspect its nuclear facilities and conduct oversight.

However, the IAEA also wants to look into allegations that Iran had conducted research into nuclear weapons production at least until 2003, which included explosives test at its Parchin military facility.

IAEA officials had reportedly obtained samples from Iran’s Parchin facility, though the environmental samples were reportedly taken without international inspectors at the time. “Iranian experts took samples from specific locations in Parchin facilities this week without IAEA’s inspectors being present,” Behrouz Kamalvandi, head of Iran’s nuclear program, told local media, cited by Reuters. “They followed regulations and standards and the samples were given to IAEA’s experts.”

However, according to early reports from a Reuters correspondent, Amano had indicated he was present when the Parchin samples were taken, seemingly contradicting Tehran’s statements.

An earlier draft of the agreement, obtained by the Associated Press, said that Amano’s visit would not be carried out as an official participant in an IAEA probe but rather a “courtesy” extended by Tehran. The draft also reportedly said that Amano would only visit Parchin after the site had been probed.

The reports of sample gathering come less than a month before an Oct. 15 deadline for the IAEA to finish its fact-finding probe. A final U.N. assessment is due in December, and the negotiations between Iran and the world powers -- which will determine the fate of international sanctions against the Middle Eastern country -- are set to be finalized by next July.