The latest sign comes with an announcement yesterday that Tehran has successfully used biotechnology to convert uranium ore mined in Iran's central desert region into a concentrated form of uranium.
The concentrated uranium -- known as "'yellowcake" -- is used in an early stage of the complex process of producing nuclear fuel.
State television provided few details of the biotechnology technique, other than to say it is more efficient and less expensive than Iran's previous method of using acid.
Biotechnology techniques involve the use of microscopic organisms to convert material through organic processes from one form to another.
Shannon Kile, a nuclear expert at the Stockholm International Peace Research Institute in Sweden, said the new technology does not by itself bring Iran closer to mastering the sensitive process of uranium enrichment -- the focus of the Iranian nuclear crisis.
"The process that was announced yesterday is the very first step when the uranium is actually extracted from the mine and then is converted into yellowcake," Kyle said. "That's the beginning step of any process in the subsequent nuclear fuel cycle, so this is really the very first step at the front end of the fuel cycle."
But the analyst said the development is important because it shows that Tehran is determined to master less sensitive elements of the fuel cycle, despite European and U.S. requests that it abandon all activities related to uranium enrichment.
"I think it is important to see the announcement by the Iranians as indications that they are going to move ahead with their civilian nuclear-fuel cycle program and that they have no intentions of suspending all the activities in that program, as has been requested by the Europeans and the Americans," Kyle said.
The news of Iran's latest activity comes two months after Iran rejected an offer by three European Union states of technology and trade assistance in exchange for Tehran abandoning all activities related to uranium enrichment. At the same time, Tehran broke its agreement with the European states to suspend such work while the two sides held talks.
French President Jacques Chirac on 29 August warned Iran that -- unless those talks resume -- Western states will have no choice but to ask that the Iranian nuclear crisis be referred to the UN Security Council.
"There is room for dialogue and negotiation [with Iran]," Chirac said. "We urge Iran to show a spirit of responsibility to reestablish cooperation and trust, without which -- and I would regret that -- the Security Council will have no choice but to examine the issue."
Iran broke its agreement with France, Britain, and Germany -- the so-called Euro 3 -- by resuming some nuclear work at the Uranium Conversion Facility in Isfahan in early August. Work at the facility includes the processing of uranium yellowcake.
All activities at the Isfahan plant had been suspended since November 2004 as part of the Iran-EU agreement to hold nuclear talks.
The U.S. State Department yesterday called on Iran to "reengage with the Euro 3, and not only reengage but take the deal that has been offered them."
Spokesman Sean McCormack called the European offer "a good deal."
Iran said on 28 August that it no longer considers the three EU states its sole negotiating partners in trying to end the international crisis over its nuclear activities. Iranian officials have indicated Tehran now may try to broaden the talks to include nonaligned countries.
The pressure for Iran to resume the talks is mounting, ahead of a 3 September meeting in Vienna of the board of governors of the UN's nuclear watchdog -- the International Atomic Energy Agency (IAEA).
The IAEA is charged with monitoring Iran's compliance with international treaty obligations permitting it to develop civilian nuclear technology but prohibiting activities that could lead to nuclear-weapons development.
Iran's most controversial nuclear-processing activities have been its efforts to master uranium enrichment, which can be used to produce fuel for nuclear reactors or -- at high levels of enrichment -- weapons-grade material.
Those efforts, conducted in secret, were uncovered in 2002, precipitating the Iran nuclear crisis. Since then, Iran has said it is not engaged in uranium enrichment but will not give up its right to master the technology, along with all other stages of the fuel cycle.
Tehran maintains it is only developing a nuclear program to meet its electricity needs.
Iran's new minister of defense and armed forces logistics, General Mustafa Mohammad-Najjar, said yesterday that "as our Supreme Leader [Ayatollah Ali Khamenei] has said, the non-peaceful use of nuclear technology is religiously forbidden."
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For RFE/RL's complete coverage of the controversy surrounding Iran's nuclear program, see "Iran's Nuclear Program."