Republicans back tough Iran line; Trump says nothing off table

Flynn insisted that the missile test was "in defiance of UN Security Council Resolution 2231", which calls on Iran not to test missiles capable of delivering a nuclear weapon.

Iran confirmed it had tested a new missile but said it did not breach a nuclear accord reached with world powers or a U.N. Security Council resolution that endorsed the pact.

The Islamic Republic will "vigorously continue with its missile activity", a top Iranian official declared on Thursday - a day after the Trump administration put Tehran "on notice" - the regime-aligned Tasnim news agency reported.

"We are going to take appropriate action", the official said, repeatedly asserting that the administration was "in a deliberative process" about future steps.

A spokesman for the U.S. Central Command clarified that it has "not been asked to change anything operationally" and that, for now, changes were "still at a policy level".

While Iran's supreme leader usually prefers "to respond to threats by threats lest silence is interpreted as weakness", Iran will likely try to sound more measured in its reactions than the Trump administration, according to Ali Vaez, senior Iran analyst at the International Crisis Group.

U.S. officials stressed the move was separate from the worldwide Iran nuclear deal.

The other possible action the United States could take would be to "snap back" a broad array of economic sanctions against Iran, the removal of which was the carrot for Tehran to agree to dismantle its nuclear weapons program.

Sen. Bob Corker (R-Tenn.), chairman of the Foreign Relations Committee, says it's about time the United States started pushing back on Iran over its ballistic missile launches as well as what Iran is doing in Yemen, Syria and elsewhere in the Middle East.

"We do not believe that the reimposition of sanctions would lead to an abrupt cut in Iranian exports, but the threat of new U.S. sanctions will likely slow the pace of investment needed for Iran's oil sector to mitigate the decline from existing oil fields", Barclays said in a note in January.

"I am very encouraged by the seriousness with which President Trump is approaching the full range of threats Iran poses to American interests".

President Donald Trump has been critical of last year's nuclear agreement that eased economic sanctions on Iran in return for assurances that Iran won't pursue nuclear weapons. Flynn informed the country that they were "on notice" while slamming the Obama administration for being too soft.

The US statement was created to send a message to Tehran to stop its provocative behaviour, said a senior US official, who spoke about the remarks on condition of anonymity.

He added: "Iran has been formally PUT ON NOTICE for firing a ballistic missile".