The White House put Iran "on notice" on Wednesday for test-firing a ballistic missile and said it was reviewing how to respond, taking an aggressive posture toward Tehran that could raise tensions in the region.
While the exact implications of the US threat were unclear, the new administration signalled that President Donald Trump intended to do more, possibly including imposing new sanctions, to curb what he sees as defiance of a nuclear deal negotiated in 2015 by then-President Barack Obama.
The tough talk commits the administration to back up its rhetoric with action, which could cast doubt on the future of the Iran agreement and sow further uncertainty in the Middle East, experts said.
Officials declined to say whether the military option was on the table, but Pentagon spokesman Christopher Sherwood said, "The US military has not changed its posture in response to the Iranian test missile launch."
A fiery statement from Trump's national security adviser, Michael Flynn, marked some of the most aggressive rhetoric by the administration that took office on January 20.
More confrontational approach?
Flynn made clear that Obama's less confrontational approach towards Iran was over.
He said that instead of being thankful to the United States for the nuclear deal, "Iran is now feeling emboldened."
The launch and an attack on Monday against a Saudi naval vessel by Iran-allied Houthi militants off the coast of Yemen underscored "Iran's destabilising behaviour across the Middle East," he added.
Iran confirmed it had tested a new missile but said it did not breach a nuclear accord reached with world powers or a UN Security Council resolution that endorsed the pact.