Michael Flynn, a retired lieutenant general and Trump's national security adviser. Lauren Victoria Burke/AP Photo On Wednesday, President Donald Trump's national security adviser, Michael Flynn, made a cameo at the White House's press briefing to issue a stern rebuke of Iran.

"Recent Iranian actions involving a provocative ballistic missile launch and an attack against a Saudi naval vessel conducted by Iran-supported Houthi militants underscore what should have been clear to the international community all along about Iran's destabilizing behavior across the entire Middle East," Flynn said, referring to Monday's Houthi attack that killed two sailors on a Saudi ship.

Saudi Arabia leads a military coalition of Gulf states involved in bombing Iranian-backed Houthi rebels in Yemen. While the Saudis support the internationally recognized government of Yemen, they stand accused of war crimes in their massive air campaign there.

Flynn said Iran had violated UN Security Council Resolution 2231, which prohibits Iran from designing missiles capable of delivering nuclear weapons. But a European Union representative said on Tuesday at the UN Security Council that Iran's test did not violate the resolution.

Experts have told Business Insider that Iran's missile launches violate the spirit of the resolution but that the language of the resolution remains ambiguous on missile testing.

The fact that no definite criteria exist for differentiating conventional ballistic missiles from nuclear-capable ones further muddles the issue of whether Iran violated the resolution.

Flynn pointed to the series of incidents at sea where Iranian naval vessels have harassed US ships. Iranian-backed Houthi militants in Yemen have also attacked ships from the US and Saudi Arabia.

"In these and other similar activities, Iran continues to threaten US friends and allies in the region," said Flynn.

Flynn criticized the Obama administration's handling of Iran, saying Trump found its moves "weak and ineffective."

Iranian-made missiles at Holy Defence Museum in Tehran. Reuters

Flynn came to a forceful yet vague conclusion.

"As of today, we're officially putting Iran on notice," he said.

Flynn's comments echo what Lawrence Brennan, a Fordham University maritime law professor and former US Navy commander, told Business Insider on Monday. Essentially, the Houthi attack on a Saudi ship using suicide boats may change the calculus for the US Navy operating in the region, he said.

"This attack is likely to impact US naval operations and rules of engagement in nearby waters," said Brennan, who said Iranian ships frequently harass and sail close to US Navy ships.

Brennan suggested that in light of the recent suicide boat attacks, the US Navy should consider shooting Iranian or other hostile vessels that get too close.

Iran's fast-attack craft, the type repeatedly used to harass US Navy ships. Fars News Agency Photo via USNI News

"The overarching duty of self-defense mandates revision of the ROE to provide a sufficient 'bubble' to prevent the risk of a suicide attack, particularly from swarming boats," Brennan said in an email to Business Insider.

This suggestion fits in line with Trump's expressed intention to deal with Iran more forcefully.

"With Iran," Trump said while campaigning in Florida in September, "when they circle our beautiful destroyers with their little boats and they make gestures at our people that they shouldn't be allowed to make, they will be shot out of the water."