Iran says it has begun further enriching uranium, a move some Western nations say should be met with sanctions. But China continues to push for a diplomatic solution.
Iranian envoy Ali Asghar Soltanieh says he has informed the International Atomic Energy Agency of his country's latest move.
"I reflected to the agency the intention of the government of the Islamic Republic of Iran to start its nuclear enrichment activities of uranium up to 20 percent, I repeat up to 20 percent, in order to produce required fuel for Tehran's research reactor," Soltinieh said.
Iran's Foreign Ministry defended the enrichment, saying it is part of the nation's peaceful nuclear program.
Spokesman Ramin Mehman-Parast argued enrichment is not inconsistent with trading fuel abroad, since, he said Tehran is ready to discuss the matter if "opposing" parties are ready.
Those opposing parties, in particular the United States, are pushing to sanction Iran for further enriching its uranium stockpile instead of accepting an offer to have it boosted overseas.
The IAEA has offered to send the uranium to Russia and France for enrichment and conversion into fuel rods for the Tehran reactor.
The move would largely foil, at least for the time being, any Iranian plans to seek nuclear weapons. Tehran denies its nuclear program has a military component.
A U.S. Defense Department spokesman said the United States will try to get new U.N. sanctions placed on Iran within weeks.
France, another member of the U.N. Security Council, has said it also favors stronger action. Russian officials have also shown more willingness to consider what would be a fourth round of sanctions.
But veto-wielding China is urging more diplomacy.
Foreign Ministry spokesman Ma Zhaoxu expressed hope all involved will work to advance "dialogue and negotiation."
China, with strong business ties to Iran, has long opposed imposing more restrictions.
Iranian envoy Soltinieh says Tehran has other options for the IAEA to consider.
"We are ready to separate the required material for exchange," Soltinieh said. "We are going to separate it from Natanz, [have it] existing in a separate container, under the seals of the IAEA, and under the custody of the IAEA in Iran. [This] means that we are not going to use it for any purpose and it will stay in Iran until the fuel is ready for the swap and exchange."
Soltinieh says this proposal has been ignored.
It is not clear Tehran can actually boost uranium from its current state of under five percent enrichment to the 20 percent needed for a reactor. Its processing program would need to be adjusted first, and there have been no reports that has been undertaken.
Iranian officials say the process is being overseen by U.N. inspectors.
If Tehran could push the enrichment to 20 percent, scientists say raising it to weapons grade would not be that much more difficult.