US President Donald Trump's National Security Advisor has accused the Iranian government of "malign actions" after a missile test.
Without elaborating, Michael Flynn told White House reporters: "As of today, we are officially putting Iran on notice."
Washington earlier declared the test to be "absolutely unacceptable".
Iran confirmed on Wednesday it had tested a missile over the weekend, but denied violating a UN Security Council resolution.
Mr Flynn did not provide any further details of what actions the US may be planning in response to the test, which Pentagon officials say failed upon re-entry into the earth's atmosphere.
The launch prompted the US to accuse Iran of violating UN resolution 2231, which "calls upon" Iran not to "undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons".
As part of its final negotiations for the 2015 nuclear agreement with six world powers, Tehran agreed to an eight-year extension of the UN ban on ballistic missile development.
During the White House daily press briefing, Mr Flynn did not accuse Tehran of violating that nuclear accord.
But the national security adviser did describe the Obama administration-brokered deal as "weak and ineffective".
"Instead of being thankful to the United States for these agreements, Iran is now feeling emboldened," he said.
He said "the Obama administration failed to respond adequately to Tehran's malign actions - including weapons transfers, support for terrorism and other violations of international norms".
Mr Flynn also pointed to a recent attack against a Saudi warship by Iranian-backed Houthi militants as evidence of "Iran's destabilising behaviour across the Middle East".
During Mr Trump's campaign for president, he frequently attacked the nuclear pact with Iran, vowing to "dismantle the disastrous deal".
In December 2016 Iranian President Hassan Rouhani told an audience at the University of Tehran that he would not allow Mr Trump to "rip up" the deal, Reuters news agency reported.
On Wednesday Iranian Defence Minister Hossein Dehghan stood by their missile test.
"We have previously announced that we will execute the programmes we have planned in production of defence equipment meant for our national interests and objectives," Iranian media quoted him as saying.
"Nobody can influence our decision. We will not allow foreigners to interfere in our defence affairs."