"It is not at all rational to say that Iran should not produce (isotopes and uranium) and stop its (enrichment) plant and that they will provide its needed medicine," ministry spokesman Ramin Mehmanparast told ISNA news agency.
"We will not examine offers which lead to the shutting down of Tehran reactor," said the spokesman, in an almost word-for-word repetition of a statement he made on February 10.
Iran started enriching uranium to 20 percent on February 9 to fuel its Tehran research reactor making medical radioisotopes amid international concern over its atomic ambitions.
The move comes as world powers seek to convince Iran to accept a UN-brokered deal to supply Tehran with nuclear fuel for the reactor in exchange for its low-enriched uranium being taken out of the country.
The United States, Russia and France on Tuesday said in a letter to the International Atomic Energy Agency (IAEA) that Iran's escalation of its uranium enrichment further undermined international trust in its nuclear drive.
The three said they "recognise the need in Iran for medical radioisotopes" which are "available on the world market and could be obtained as a responsible, timely and cost effective alternative to the IAEA's proposal."
Amid the threat of new sanctions President Mahmoud Ahmadinejad said on Tuesday that negotiations over the IAEA-drafted nuclear fuel exchange were "not closed yet."
He expressed readiness to buy the material from abroad, even from Iran's arch-foe the United States.
Echoing the president's comments, Mehmanparast said that Iran would "examine the issue of buying 20 percent enriched uranium or even an exchange (of uranium) under conditions desired by our country."
"But in the absence of mutually-agreed proposals, we are losing time, the reactor fuel is running out and 850,000 patients await its medical products," the spokesman said.
Ahmadinejad indicated Tehran could suspend higher grade enrichment if world powers supplied it the required fuel for the reactor.
