An International Atomic Energy Agency report detailing Iran's efforts to develop a nuclear weapon is "alarming," the US State Department said Wednesday, dpa reported.
The report on Tuesday provided the clearest indications yet that Iran has been developing nuclear arms, detailing a large number of nuclear-related projects and experiments, some of which might be ongoing.
Tehran maintains that its nuclear programme is for peaceful uses including energy generation.
State Department spokesman Mark Toner said the IAEA report raises further questions about Iran's nuclear programme and backs up US allegations that Iran has a weapons programme.
"These are very serious allegations, serious charges," he said. "And it's incumbent on Iran to at last engage with the IAEA in a credible and transparent manner to address these concerns."
The US is consulting with its allies on how to respond and will further discuss the report next week at an IAEA board of governors meeting, Toner said.
He noted existing UN sanctions on Iran, but said the US would study "ways to impose additional pressure on Iran."
"Let's be clear that the onus here is on Iran to address these questions, very serious questions, raised by not America, not the United States, but the international community, about the intent of its nuclear programme," Toner said.