Senior US congressional Republicans say they will support new sanctions on Iran, and President Donald Trump says "nothing is off the table" in dealing with Tehran, in the wake of its test-firing of a ballistic missile.
Iran has confirmed it had tested a missile over the weekend, but denied violating a UN Security Council resolution on its nuclear activities.
Washington earlier declared the test to be "absolutely unacceptable" and Mr Trump told reporters on Thursday "nothing is off the table" in dealing with Iran.
Speaker of the House of Representatives Paul Ryan said he would support more sanctions, and that the United States should stop "appeasing" Iran.
"I would be in favour of additional sanctions on Iran," Mr Ryan said.
"I'd like to put as much toothpaste back in the tube as possible. I think the last administration appeased Iran far too much."
Republican lawmakers said they were working with the administration to push back on Iran as much as possible, without tearing up the international nuclear deal announced in July 2015.
"I think there's a lot that we can do, now, that we were unable to do before to push back against Iran," Senate Foreign Relations Committee chair Senator Bob Corker told Reuters.
Mr Corker said his committee was "in the early stages" of working on legislation related to the nuclear issue.
Congressional aides said Mr Trump's administration had already begun looking at actions it could take without waiting for Congress.
For example, Mr Trump could impose sanctions authorised by laws passed but not put into effect by the Obama administration, which reached the agreement between Iran, the United States and other world powers.
Mr Corker said he had discussed Iran at the White House with Mr Trump's national security adviser, Michael Flynn, just before Mr Flynn issued a warning that Washington was putting Iran on notice for its "destabilising activity."
Mr Corker said the Trump administration would take a stronger stance against Iran, although he did not expect its actions would bring an end to the international nuclear deal.
"The administration, thankfully, is going to follow through on appropriately holding Iran accountable for the violations that are taking place."
Highlighting the Trump administration's more aggressive tone against Iran, Mr Trump sent messages on Twitter on Wednesday and Thursday targeting the Islamic republic and criticising the nuclear pact.
Iran has been formally PUT ON NOTICE for firing a ballistic missile.Should have been thankful for the terrible deal the U.S. made with them!— Donald J. Trump (@realDonaldTrump) February 2, 2017
Iran was on its last legs and ready to collapse until the U.S. came along and gave it a life-line in the form of the Iran Deal: $150 billion— Donald J. Trump (@realDonaldTrump) February 2, 2017
Another senior Republican foreign policy voice, Senator Lindsey Graham, told CNN he thought Mr Trump should go to Congress to request additional sanctions for a range of activities in the Middle East, including a ballistic missile test last weekend, which he said were not in US interests.
"The world should not only condemn Iran but we should have multi-national sanctions against the regime for their continued violation of the UN Security Council resolutions regarding their missile program," Graham said.
Ali Akbar Velayati, a top adviser to the country's Supreme Leader Ali Khamenei, has dismissed the comments, saying: "This is not the first time that an inexperienced person has threatened Iran."