"We're going to make sure we have all options available to the president," White House national security spokesman John Kirby told a briefing in Washington.

"We certainly have not changed our view that we will not allow Iran to achieve a nuclear weapons capability."

Iran meantime publicized that it had moved ahead on uranium enrichment that Western governments worry is part of a covert nuclear weapons program.

"Iran has started producing uranium enriched to 60 percent at the Fordo plant for the first time," Iran's ISNA news agency reported, a development then confirmed by Atomic Energy Organisation of Iran chief Mohammad Eslami.

An atomic bomb requires uranium enriched to 90 percent, so 60 percent is a significant step towards weapons-grade enrichment.

The heavily protected Fordo plant around 110 miles (190 kilometers) south of Tehran was built deep underground in a bid to shield it from air or missiles strikes by Iran's enemies.

Iran in April announced that its older facility at Natanz, southeast of Fordo, had ramped uranium enrichment to 60 percent.