"I agree to talks with 5-plus-1," Mousavi told journalists from international news networks.

But Mousavi said Tehran would continue its nuclear programme.

"We will not give (up) anything for having the technology. What will be negotiated is finding ways (to guarantee) that our nuclear programme will not deviate towards a weapons plan," the moderate candidate said.

Mousavi's stand is the opposite to incumbent conservative President Mahmoud Ahmadinejad, who is seeking a second term in office in the June 12 polls.

On Monday, Ahmadinejad rejected talks with the 5-plus-1 group over Tehran's nuclear issue.

"We have said this before and we are saying it right now, that we will not talk about the nuclear issue with those outside the IAEA (International Atomic Energy Agency)," Ahmadinejad told journalists.

EU foreign policy chief Javier Solana held talks with Iranian nuclear negotiator Saeed Jalili in April about discussions with the group of world powers known as the P5-plus-1 on Tehran's controversial atomic activities.

Solana has been authorised by the six powers -- UN Security Council veto-wielding permanent members Britain, China, France, Russia and the United States plus Germany -- to discuss the issue with Tehran.

In April, Iran said it was ready for "constructive dialogue" with the world powers, while at the same time vowing to continue with its nuclear activities which have been the subject of an IAEA investigation for several years.

Global powers fear Iran's nuclear drive could be a cover for efforts to build an atomic bomb, but Tehran insists it is aimed purely at generating electricity for a growing population.

Mousavi, who is backed by several reformist groups in the presidency race, said holding "talks and debates with US" was not a "taboo" for him despite the pressures which Washington exerted on Tehran.

"Every year they renew sanctions against Iran and pressure Iran's economy ... Whenever we have to buy airplanes, the US creates problems for us," he said, urging Washington to show more "positive" signs towards Tehran.

"The relation with US is complicated and it takes time. Their changing their tone is effective. I see a positive trend that there is a possibility to become better," he added.

The two countries have had no diplomatic relations since the year after Iran's 1979 Islamic revolution which toppled the US-backed shah.

But US President Barack Obama's administration has made diplomatic overtures towards Iran in a bid to halt the Islamic republic's sensitive nuclear activities.

Mousavi, meanwhile, expressed optimism on his chances of winning the presidential election.

"There is no reliable survey, but some show that there is an upward swing in my favour and so I am very hopeful of winning," Mousavi said.

"The drop in voting favouring Ahmadinejad will go in my favour since my slogan is that I am a reformist who resorts to principles" of the revolution, said the candidate.

He said that "irregularities" in the voting process were a concern.

"We are negotiating with the interior ministry to minimise irregularities and make sure that the government guards the people's vote (ballot boxes)," Mousavi added.

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