Dozens of anti-war activists gathered in New York's Times Square and outside the White House in Washington to protest the airstrikes carried out in Yemen.
In Times Square, chants such as "Hands off the Middle East," "Hands off Yemen," and "Hands off Gaza" were heard, while protesters outside the White House waved Palestinian flags and carried "Free Palestine" and "Stop bombing Yemen" banners.
The US and its allies, in a joint statement, said that the strikes were an act of defense and there was no intent to escalate tensions. But protesters worry that the move will widen the war in Gaza.
US, UK launch 'defensive action' against Houthis in Yemen
The United States, the United Kingdom and their allies have carried out strikes against sites used by the Houthi rebel group in Yemen in "defensive action" after attacks on shipping in the Red Sea.
US officials said targets included logistical hubs, air defense systems and weapons storage locations. US media reported that the strikes involved fighter jets and Tomahawk missiles.
The Houthis are backed by Iran and control large swathes of western Yemen, including the capital, Sanaa.
In a statement, US President Joe Biden said the airstrikes were carried out with "support" from Australia, Bahrain, Canada and the Netherlands.
In recent weeks, Houthi rebels have launched numerous attacks on international ships in the Red Sea in reaction to Israeli military operations in the Gaza Strip.
A Houthi official vowed retribution for the attacks.
"America and Britain will have to prepare to pay a heavy price and bear all the dire consequences of this blatant aggression," Deputy Foreign Minister Hussein Al-Ezzi said, according to local media.
Biden says US 'will not hesitate' to act further
US President Joe Biden, in a statement, said he "will not hesitate" to order further military action against Iran-backed Houthis in Yemen if required, and that Washington and its allies "will not tolerate attacks on our personnel or allow hostile actors to imperil freedom of navigation."
"Today, at my direction, US military forces — together with the United Kingdom and with support from Australia, Bahrain, Canada, and the Netherlands — successfully conducted strikes against a number of targets in Yemen used by Houthi rebels to endanger freedom of navigation in one of the world's most vital waterways," Biden said.
He said the airstrikes on Houthi-controlled cities in Yemen were a "direct response" to "unprecedented" attacks by the Houthis. This included the use of an anti-ship ballistic missile "for the first time in history."
"These attacks have endangered US personnel, civilian mariners, and our partners, jeopardized trade, and threatened freedom of navigation," Biden said, adding, "I will not hesitate to direct further measures to protect our people and the free flow of international commerce as necessary."
More reactions to the airstrikes in Yemen
Hours after the US and its allies carried out airstrikes on Houthi-controlled cities and targets in Yemen, a joint statement by the US, Britain, Australia, Bahrain, Canada, Denmark, Germany, Netherlands, New Zealand and South Korea said the "aim remains to de-escalate tensions and restore stability in the Red Sea."
In a separate statement, British Prime Minister Rishi Sunak confirmed that "limited, necessary and proportionate action in self-defense" had been taken and that repeated aggression against international shipping in the Red Sea "cannot stand."
"Despite the repeated warnings from the international community, the Houthis have continued to carry out attacks in the Red Sea, including against UK and US warships just this week," Sunak told British media.
"The United Kingdom will always stand up for freedom of navigation and the free flow of trade," he said.
Australian Defense Minister Richard Marles said his country had provided personnel support for the US and UK strikes in Yemen.
"Australia's support of these actions came in the form of personnel in the operational headquarters," he told reporters. "Australia will continue to support any actions which assert the global rules-based order."
Meanwhile, Saudi Arabia, a long-time regional rival of Iran, is trying to end its involvement in a nine-year war against the Houthis, urged against escalation.
"The Kingdom of Saudi Arabia is following with great concern the military operations," a Foreign Ministry statement said, calling for "self-restraint and avoiding escalation."
