The United Nations atomic energy agency says the Iranian government has slowed its pace of uranium enrichment ahead of new nuclear talks with six world powers.
In a report Thursday, the International Atomic Energy Agency said that no major new components have been installed at the unfinished Arak reactor, a heavy water facility that was due to come online next year.
Arak, which when operational could produce plutonium, was a major sticking point in talks between Iran and the powers in Geneva last week.
The IAEA report stated that Iran had installed only four first-generation centrifuges at the Natanz plant- machines used to refine uranium - but not all of the installed centrifuges are operating.
The quarterly IAEA report was the first that included developments since Hassan Rouhani took office as president early in August, prompting a diplomatic opening between Iran and six world powers.
It also showed that Iran's stockpile of higher-grade enriched uranium had risen by about 5 percent to 196kg since August, largely due to a temporary halt in converting the material into reactor fuel.
But the amount of uranium gas enriched to a fissile concentration of 20 percent still remained below the roughly 250kg needed for a bomb if processed further - an amount that Israel has indicated is a "red line" that could trigger military action against Iran.
Obama against more sanctions
Meanwhile, the US president Barack Obama urged members of Congress not to add new sanctions against Iran.
Obama said that if Iran can't deliver on future promises and commitments, "the sanctions can be ramped back up".
He said there was no need to add new sanctions on top of sanctions already in place that have "crippled" Iran's economy.
However, Israel's prime minister, Benjamin Netanyahu, said that he was he was "not impressed" by the IAEA report on Iran.
"They've got enough facilities, enough centrifuges to develop and to complete the fissile material which is at the core of an atomic bomb," he said.
Iran and the United States, Russia, China, Britain, France and Germany are looking to limit Tehran's nuclear capacities. Tehran wants relief from economic sanctions. They meet again next week after talks last week.