Iran rejects Western pressures over its nuclear activities and will never give up its rights, Tehran's chief nuclear negotiator said Thursday ahead of crunch talks with world powers in Baghdad next week.

"If we participate in the negotiations... it is because of our resistance (to Western powers). Thanks to our resistance, we have defended the rights of the Iranian people," Saeed Jalili said in a speech broadcast on local television.

"The Iranian people will never give up even an iota of their rights," Jalili added, in reference to the Islamic republic's nuclear drive which the West suspects is masking a weapons programme. Tehran vehemently denies the charge.

After a 15 month hiatus, Iran and the P5+1 powers -- Britain, China, France, Russia and the United States plus Germany -- held their first talks in Istanbul in mid-April, which were described as "positive."

The parties agreed to more in-depth discussions in Baghdad on May 23.

"I advise Western officials against making calculated mistakes. In Baghdad, we can negotiate for cooperation on the basis of respect for Iran's undeniable rights," Jalili said.

"The path chosen by our country is a path of no return. The (West) would like to block Iran's progress in the nuclear domain, but they have failed. Iran today has become a nuclear power," he added.

"To those who say that time is running out for dialogue, I reply: What is running out is the policy of pressuring Iran, because this strategy has not yielded the results" expected by world powers.

The United States and the European Union have tightened economic sanctions on Iran, imposing tough restrictions on its vital oil industry, to pressure it over its disputed uranium enrichment programme.

US President Barack Obama warned Iran in March that time was running out to resolve the standoff through diplomacy.

But Jalili was defiant on Thursday, insisting that sanctions and international pressure were not affecting Iran's determination.

"Those who think they can pressure Iran with these sanctions are wrong... because the sanctions have allowed us to make progress," he said.

He argued that the conditions imposed on Iran at talks in Geneva in 2009 for the delivery of uranium enriched to 20 percent for its Tehran research reactor had in fact forced it to produce the nuclear fuel itself.

"We told them: 'If you do not give us the fuel, we will produce it ourselves.' I will never forget the smiles from certain members of the P5+1.

"But in less than two years we produced the fuel, and we are using it today."

Iran currently enriches uranium to 3.5 percent and to 20 percent. The former it says is to power its Bushehr nuclear electricity plant and the latter it says is to generate medical isotopes in its Tehran research reactor.

Uranium has to be enriched to 90 percent or above for use in an atomic bomb.

Several Iranian officials have in recent weeks hinted that Tehran may under certain conditions suspend its drive of enriching uranium to the 20 percent level.

Tehran says it wants international acceptance of its right to peaceful nuclear activities, for sanctions to be lifted and for the threat of US and Israeli military action to disappear.