The US gave the Houthis a final warning. The Iran-backed rebels answered with their biggest-ever missile and drone attack.

• The US appeared to give the Houthi final warning to stop their attacks on international shipping.
• Days later, the Iran-backed rebels launched their biggest missile and drone attack yet. 
• The assault was followed by more warnings from the West — then another Houthi attack on Thursday.

The US and its allies ushered in the new year by delivering a stern ultimatum to the Houthis: stop attacking international shipping lanes off the coast of Yemen or face serious consequences.

But just a few days later, the Iran-backed rebels answered with their largest-ever missile and drone onslaught, forcing the US and UK militaries to engage the threats and prompting a new wave of warnings from the two countries.

The Tuesday attack, during which more than 20 munitions were fired and shot down, has renewed questions about whether the US or its allies will take a more aggressive approach to the dilemma and strike the Houthis directly in Yemen, an option that Washington has been considering for weeks now.

"I'm not going to telegraph or preview anything that might happen," US Secretary of State Antony Blinken told reporters in Bahrain Wednesday, adding that "if this continues as it did yesterday, there will be consequences."

Over the past few months, the Houthis have launched scores of attacks targeting strategic waterways off the coast of Yemen, mainly the Red Sea, drawing engagement from American, British, and French warships. The rebels have claimed that their actions are directly related to the Israel-Hamas war, although US officials have asserted that their provocations are threatening countries from around the world.

With these attacks, the Houthis have turned an important global shipping route into a dangerous voyage, prompting international companies to reroute their vessels — driving up the costs and timelines for the movement of critical goods. In mid-December, the Pentagon announced a multinational task force with the hopes of restoring freedom of navigation through the critical corridor.

But the attacks have not let up. One particular incident on Dec. 31 was even an escalation, turning deadly for the Houthis after US Navy helicopters responded to an assault by the rebels.

A few days later, on Jan. 3, the US and more than a dozen allies issued a strongly-worded statement condemning the Houthis, demanding an end to their provocations, and warning the rebels against further incidents.

"Ongoing Houthi attacks in the Red Sea are illegal, unacceptable, and profoundly destabilizing," the statement read. "The Houthis will bear the responsibility of the consequences should they continue to threaten lives, the global economy, and free flow of commerce in the region's critical waterways."

The following day, a senior Biden administration officials told reporters that they "would not anticipate another warning" for the Houthis when asked about a US response.

"I think this statement speaks very much for itself," the official said. "It's a very clear warning."

The Houthis appeared to respond to this warning by launching their largest-ever attack on Tuesday, firing a mix of weapons toward international shipping lanes in the southern Red Sea, where dozens of merchant vessels were operating. US Central Command, or CENTCOM, said 18 one-way attack drones, two anti-ship cruise missiles, and one anti-ship ballistic missile were shot down by a combined effort of American and British naval assets, and there were no reported injuries or damage.

What followed on Wednesday were more warnings from the West.

"The UK alongside allies have previously made clear that these illegal attacks are completely unacceptable and if continued the Houthis will bear the consequences," UK Defense Secretary Grant Shapps said in a statement. "We will take the action needed to protect innocent lives and the global economy."

"We will not hesitate to take further action to deter threats to freedom of navigation in the Red Sea," Barbara Woodward, the UK's ambassador to the United Nations, said in a statement.

"We've warned them," White House National Security Council spokesperson John Kirby said at a briefing, adding that the Houthis will "bear the consequences" if they don't stop their attacks.

However, these warnings appear to have done little to deter the Houthis, who fired another anti-ship ballistic missile into international shipping lanes off the coast of Yemen on Thursday. Again, there were no reported injuries or damage, CENTCOM said.

The US has reportedly been considering options to strike back at the Houthis in Yemen for weeks now, although the Biden administration has repeatedly signaled its desire to avoid escalating the situation given the widespread tensions and violence across the Middle East that have emerged in the wake of the Israel-Hamas war. Retaliatory strikes against the Houthis would not be unprecedented — the Pentagon did so in 2016 following attacks by the rebels — but they would be escalatory.

A former top US military commander previously told Business Insider that the Houthis are particularly dangerous because they're trying to play an outsized role among Iran's regional proxy groups, adding that their provocations could require some kinetic action from the Pentagon like strikes on shore-based missile or radar sites.

The Houthis, meanwhile, are not the only Iranian proxy group that has clashed with the US since the outbreak of the Israel-Hamas war. Tehran-backed militias have carried out at least 125 attacks on American forces in Iraq and Syria over the past three months, which have led to retaliatory strikes in both of those countries.