A UN Security Council deadline for Iran to suspend uranium enrichment expires this week.
Beyond that, Ali Larijani, the top Iranian nuclear negotiator, on Tuesday also renewed the country's vow to end co-operation with the UN nuclear watchdog, the International Atomic Energy Agency, and said increasing pressure on Iran would only stiffen its resolve.
"If you take harsh measures, we will hide this programme. If you use the language of force, you should not expect us to act transparently," Larijani said, adding that Western countries on the IAEA board "have to understand they cannot resolve this issue through force".
Separately, Iran's supreme leader Ayatollah Ali Khamenei issued the offer to transfer nuclear technology as he met with Omar al-Bashir, the Sudanese president.
The US secretary of state, who was visiting Greece and Turkey, fired back almost immediately.
"Iranians can threaten, but they are deepening their own isolation," Condoleezza Rice said.
Iran's defiant stance appeared to stem in part from opposition to sanctions by Russia and China, both permanent, veto-holding members of the Security Council.
"We see no alternative to the negotiations process," Sergei Ivanov, the Russian defence minister, was quoted as saying by the Interfax news agency while in Beijing for a regional anti-terrorism meeting.
Qin Gang, a Chinese Foreign Ministry spokesman, urged all parties "to show flexibility", saying the international community should not abandon efforts for a peaceful settlement.
Khamenei said Iran is prepared
to transfer nuclear knowledge
"Iran's nuclear capability is one example of various scientific capabilities in the country. ... The Islamic Republic of Iran is prepared to transfer the experience, knowledge and technology of its scientists," Khamenei told al-Bashir.
Al-Bashir said last month that his country was considering a nuclear programme to generate electrical power.
Such a technology transfer would be legal as long as it is between signatory-states to the non-proliferation treaty, and the IAEA was informed.
Word of the transfer offer became public by the time Rice reached Ankara, Turkey, prompting her to respond yet again.
"We have to be concerned when there are statements from Iran that Iran would not only have this technology, but would share it, share technology and expertise," Rice said.