(Bloomberg) -- The US and UK launched about 70 airstrikes on Houthi targets in Yemen early on Friday in a bid to stop the Iran-backed group’s shipping attacks in the Red Sea.

The Houthis appeared undeterred, vowing to continue targeting commercial vessels and saying they would expand their campaign “very soon.” They said all US and UK interests are now legitimate targets.

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Oil prices rose more than 4%, with Brent climbing above $80 a barrel for the first time since late December.

The military action underscores the deepening fallout across the Middle East from the Israel-Hamas war, which has entered a fourth month. The Houthis started attacking ships in mid-November, ostensibly in support of Hamas, and have said they won’t back down until Israel stops fighting in Gaza.

Read More: The Spreading Fallout From Israel-Hamas War: Balance of Power

The US and its allies have worked to prevent any escalation. But the Houthis have ignored all their warnings over recent weeks to end the assaults, which have roiled global supply chains and pushed up freight costs.

The strikes came hours after US President Joe Biden’s top diplomat, Antony Blinken, ended another whirlwind tour of the region to ease tensions.

The attacks started about 2.30 a.m. Yemen time, with residents in the capital Sanaa and Red Sea port city of Hodeida reporting huge explosions. Other Houthi-held towns were hit including Saada, Taiz and Hajjah, the group said.

The Houthis said there were 73 strikes in total and that five fighters were killed. It’s unclear if any there were civilian casualties.

American and British forces hit 16 sites including airports, radar installations and storage and launch sites for drones and missiles, according to the US military.

The US attacked with jets on the USS Eisenhower aircraft carrier, as well as with Tomahawk missiles launched from a submarine and other ships. The UK sent planes from a base in Cyprus.

The Netherlands, Australia, Canada and Bahrain provided support as part of the mission, though they didn’t fire missiles.

Biden didn’t rule out more strikes. He said the move was a “clear message that the United States and our partners will not tolerate attacks on our personnel or allow hostile actors to imperil freedom of navigation in one of the world’s most critical commercial routes.”

UK Prime Minister Rishi Sunak described the hits on Yemen as “limited, necessary and proportionate” after weeks of “dangerous and destabilizing attacks” by the Houthis against shipping in the Red Sea.

Both countries said the aim was to cripple the Houthis’ ability to continue attacking commercial vessels. In the past two months, they’ve hijacked a car carrier, tried to capture others and attacked dozens with missiles and drones.

On Tuesday, the Houthis launched their largest missile and drone attack to date in the Red Sea. It prompted US and UK forces to shoot down 18 drones and three anti-ship missiles. There were no injuries or damage reported.

Many companies have rerouted their ships away from the Red Sea — which links to the Mediterranean via the Suez Canal — forcing their vessels on much longer routes around southern Africa.

The Houthis had, until now, said they were only targeting Israeli ships or those going to and from the country. Yet some vessels they’ve assaulted have no obvious links to Israel.

“It’s likely that this won’t end here,” said Jane Kinninmont, a senior research fellow at UK think tank Chatham House. “But there will be a limit on how directly the US and UK want to get involved. They will not want to be sending any troops into Yemen. What they will be doing is pressing Saudi Arabia, Egypt, Qatar and other Arab countries to join them in reining in the Houthis. There are other levers that can be used other than airstrikes.”

Saudi Arabia said it was following the latest events with “great concern,” highlighting how some of the US’s regional allies are uneasy about the strikes.

The kingdom borders Yemen and has been trying to forge a peace deal with the Houthis after failing to dislodge them from power for most of the past decade. The Houthis have attacked Saudi territory in the past, including in 2019 when they claimed a drone and missile hit that briefly knocked out half the kingdom’s oil production.

Russia and Iran, which provides funding and training to the Houthis, both said they strongly condemned the airstrikes.

“Iran has a strategy of supporting other groups to further its aims so that it can stay out of the way to some extent itself,” said Kinninmont. “It will be pleased to see the Houthis are taking action and it won’t suffer any direct costs from the airstrikes either. So, Iran probably sees this as a win-win.”

Turkey’s President Recep Tayyip Erdogan — a staunch critic of Israeli actions in Gaza — said the US and UK actions were “disproportionate” and could turn the Red Sea into a “sea of blood.”

‘Big’ Response

In a speech on Thursday, Houthi leader Abdul Malik Al-Houthi vowed a “big” response if the US and its allies proceeded with military action.

“We’ll confront the American aggression,” he said. “Any American attack won’t go unpunished.”

Read More: Who Are the Houthis Being Hit With US, UK Airstrikes: QuickTake

The strikes embroil the US in yet another fight with an Iranian proxy since the Israel-Hamas war erupted on Oct. 7. American forces have launched attacks in Syria and Iraq in recent weeks against Iranian-supported militias that have targeted American bases — so far without major casualties.

Washington also sent aircraft carriers and other ships to the region in support of Israel and to warn Lebanon’s Hezbollah militant group against a full-on attack of the Jewish state.

Hezbollah and Israel have traded fire almost daily since Oct. 7 across the Israeli-Lebanese border. While those haven’t escalated, there are growing calls within Israel for the government to act more aggressively against the group.

Hezbollah Says Top Commander Killed as Tensions With Israel Grow

The fighting in Gaza, meanwhile, continues to rage and Israeli officials say it could go on for months, if not longer. More than 22,000 people have been killed there, according to health officials in the Hamas-run Palestinian territory.

Hamas, designated a terrorist group by the US and European Union, killed 1,200 people during its October incursion into Israel.

Deterring the Houthis won’t be easy. The group, which took control of Sanaa in 2014 at the start of Yemen’s civil war, holds much of the north-west of the country. It withstood a massive bombing campaign from a Saudi-led coalition that began a year later, and remains firmly entrenched.

The US revoked its designation of the Houthis as a terrorist group in 2021 out of concern the label would harm Yemenis’ access to aid, with the conflict having devastated the country. There’s been a tentative truce since 2022, but UN-mediated talks involving the Saudis are yet to result in a formal peace deal.

Late last month, the US spearheaded the creation of a maritime task force — dubbed Operation Prosperity Guardian — whose goal was to provide security for vessels transiting the Red Sea. It’s largely restricted itself to defending ships coming under attack.

--With assistance from Courtney McBride and Dana Khraiche.

(Updates with oil market reaction in third paragraph.)

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