On Tuesday, White House spokesman Robert Gibbs said that December is "a very real deadline" for Iran to "pursue its responsibilities" on the nuclear issue.
Responding to Iran's President Mahmoud Ahmadinejad's defiance over the year-end deadline, Gibbs said while Ahmadinejad "may not recognize ... the deadline that looms, but that is a very real deadline for the international community."
Mehmanparast said that Iran rejects the December deadline for Iran to accept a deal for swapping enriched uranium with nuclear fuel, adding that the new deadline is not something new.
Tehran is still waiting for response from six major countries to its nuclear fuel swap proposal, Mehmanparast said.
Iran has proposed to swap nuclear fuel at the Iranian Kish Island to secure fuel supply for a Tehran medical research reactor and the six major countries might have a new proposal to offer, he said.
"Iran welcomes any proposal to meet the demand for fuel to the Tehran reactor," he was quoted as saying.
"Iran has adopted a crystal clear stand on its peaceful nuclear activities and the International Atomic Energy Agency (IAEA) is responsible to provide Iran with nuclear fuel based on its Charter and the Non-Proliferation Treaty," Mehmanparast said.
"If they refuse to meet our legal demand, it will be quite natural for Iran to produce 20 percent nuclear fuel for the reactor," he said.
Under a draft deal brokered by the UN nuclear watchdog, most of Iran's existing low-grade enriched uranium would be shipped to Russia and France by the end of the year, where it would be processed into fuel rods with the purity of 20 percent.
The higher-level enriched uranium would be transported back to Iran to be used in the research reactor in Tehran for the manufacture of medical radioisotopes.
Iran has rejected the deal, demanding a simultaneous exchange between low and higher level enriched uranium inside the country.
The United States and its Western allies have been accusing Iran of secretly developing nuclear weapons under the disguise of civilian nuclear power. Iran has denied the accusation and stressed its nuclear program is only for peaceful purposes.
The United States has threatened another round of UN sanctions against Iran if it does not abide by the year-end deadline.