The calls came after a new report by the UN nuclear watchdog was sent to member countries and leaked to the press concluding that "Iran has carried out activities relevant to the development of a nuclear device" even though it may still be under way.
"Today's report is yet another indication of Iran's failure to live up to its international obligations, failure to demonstrate to the international community its programme and further undermines the credibility of Iranian government statements challenging international pressure over its nuclear programme," a senior administration official told reporters hours after the report was sent to member countries.
Another senior official told reporters on condition of anonymity that the US would consult its international partners on ways to increase pressure on Iran.
"Once more obligation is on Iranian government by demonstrating to the world the nature of its programme, by answering the questions that are being raised directly by the IAEA. That is what we will be focused on," the senior administration official said.
A number of US lawmakers too ratcheted up pressure seeking strong international action against Tehran. Senator John Kerry, Chairman of the Senate Foreign Relations Committee, said the IAEA report makes it clear that Iran has not been truthful about its nuclear programme.
Though the IAEA report does not conclude that Iran has restarted the same kind of programme it had in place before 2003, the senior administration official said it raises concerns about possible ongoing research related to nuclear weapons development.
Iran dismissed the report as "baseless" but the official said the report "builds on the very troubling regime behaviour overtime: and enforces what the has been concluded on different occasions".The official said such conclusions were the reason behind the UN Security Council resolution 1949 that laid the foundation for unprecedented sanctions against Iran, and also provides for building additional pressure on the regime.
"... this report will further underscore that Iran is the only NPT signatory which is unable to convince IAEA... That further isolates Iran among the international community," the US official said.
"The United States would be consulting in coming days with its allies and partners about the next steps that we might take. It is certainly the case that we would be looking to impose additional pressure on the Iranian government... that would include additional sanctions imposed by the United States," the official said.
US and Israel have been at the forefront of demands that action be taken against Iran, with reports indicating that Israel was even contemplating a strike.Iranian President Mahmoud Ahmadinejad has also hit back at the attacks, saying yesterday that Tehran "does not need an atomic bomb" to take on the US.
"The international community must continue to stand strong and increase pressure on Iran to comply with its international obligations. Iran's leaders know what they need to do, the question is how we ensure they start doing it," Kerry said.
The Foreign Relations Committee is already planning a hearing for the coming weeks to look at this issue and other related concerns regarding Iran.
Senator Joe Lieberman said it was time for Congress to pass the new and tougher Iran sanctions legislation, which over three-fourths of the Senate has co-sponsored.
"It is time for the US and our international partners to move beyond the formulation that all options are on the table".
"Rather, it is time for an unequivocal declaration that we will stop Iran from acquiring nuclear weapons capability -- by peaceful means if we possibly can, but with military force if we absolutely must," Lieberman said.
Democrat Senator Robert Menendez said the Iranian regime is a growing threat that must be deterred and that the international community must take steps "now - not tomorrow - to stop Iran from acquiring a nuclear weapon".
"We need to respond to Iran with even tougher sanctions, make the US an Iranian oil free zone, step up sanctions on the IRGC, and sanction the Iranian Central Bank and countries like China and Russia that flaunt our sanctions and have provided critical scientific knowledge to the Iranians," Menendez said.
Senator Kirsten Gillibrand, a member of the Senate Armed Services Committee, said IAEA report should serve as a wake-up call to the world community.
"As the evidence mounts of Iran's nuclear advances, it is clear the Iranian regime is becoming an existential threat to the United States and our allies and we must act quickly to enact a new round of international sanctions," she said.
"I urge Congress to pass the Iran, North Korea, and Syria Sanctions Consolidation Act, my bi-partisan legislation that increases economic pressure on Iran.
"This strong legislation gives the President improved tools to help stop Iran's nuclear programme," Gillibrand said.
"We must cut off ties with any company that buys oil and gas from Iran's Revolutionary Guard. We must keep dangerous weapons out of the hands of all hostile nations. We must stand together and make it crystal clear - we cannot, and will not, tolerate a nuclear Iran," she demanded.