The Arak site is of concern to the West because Tehran could theoretically extract weapons-grade plutonium from its spent fuel if it also builds a reprocessing facility, potentially giving it a second route to an atomic bomb.
"Here we can do some design change ... In order to produce less plutonium in this reactor and in this way allay the worries and mitigate the concerns," Salehi said, according to a transcript of his interview with the English-language Press TV website.
"This reactor is a research reactor. It is for (the) purpose of producing radio-isotopes and making other tests," he said.
Western nations and Israel have long suspected Iran of covertly pursuing nuclear weapons alongside its civilian programme, allegations denied by Tehran, which insists its nuclear activities are entirely peaceful.
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A top US diplomat, Wendy Sherman, said earlier this week that Iran did not need some of its nuclear facilities, including the Arak reactor, in order to have a peaceful programme.
It also committed not to make further advances at its Arak, Fordo and Natanz facilities.