The UK will not hesitate to take further military action against Houthi targets in Yemen if the group continues Red Sea attacks, Prime Minister Rishi Sunak has told MPs.
Mr Sunak said the UK was not seeking confrontation with the Iran-backed group, but would continue to act in self-defence.
It follows overnight strikes with the US in Yemen.
Labour leader Sir Keir Starmer said he backed the “targeted action”.
Four RAF Typhoons and two Voyager tankers took part in a second wave of joint US-UK action against the Houthis on Monday night, following previous raids on 11 January.
They targeted two military sites used to support attacks on shipping north of Yemen’s capital, Sanaa. The prime minister said all intended targets were destroyed.
Addressing the House of Commons on Tuesday, Mr Sunak said: “We are not seeking a confrontation. We urge the Houthis and those who enable them to stop these illegal and unacceptable attacks.
“But, if necessary, the United Kingdom will not hesitate to respond again in self-defence.
“We cannot stand by and allow these attacks to go unchallenged. Inaction is also a choice.”
“Maximum care” was taken to protect civilians in the strikes, he added. No civilians have died as a result of the strikes.
Sir Keir was not briefed beforehand, but Downing Street said he and Commons Speaker Sir Lindsay Hoyle were informed while British fighter jets were in the air at about 22:00 on Monday.
Since November, the Houthis have launched dozens of attacks on commercial vessels travelling through the Red Sea, one of the world’s busiest shipping lanes.
The group says it is targeting ships linked to Israel in response to the military ground operation in Gaza. However, many of the vessels which have been attacked have no connection with Israel.
Yemen’s internationally recognised government, which is now based in Riyadh, Saudia Arabia, has condemned Houthi attacks.
The Houthis have a large supply of missiles and drones and they show every sign of continuing their attacks on shipping, undeterred by the eight US-led air strikes so far this year.
The US and UK have little choice but to continue hitting Houthi targets as long as their attacks continue – to give up now would be tantamount to ceding control of a crucial global shipping route to a proscribed terror group backed by Iran.
So far, the strikes have been precise and calibrated with minimal human casualties, but that may change.
The longer these exchanges carry on, the greater the risk of escalation. There is a real risk that in due course Yemeni civilians may die in these retaliatory air strikes, which could ignite a wave of anti-western anger across the wider Middle East.
The Houthis have said the US and UK are supporting Israel by launching strikes against the group.
But Mr Sunak said there was “no link between our actions of self-defence in the Red Sea and the situation in Israel and Gaza”.
“Those who make that link do the Houthis’ work for them,” he told MPs.
There have been at least 12 further attacks by the Houthis since 11 January, including on Monday night ahead of the latest strikes.
Incidents have increased in the Red Sea and Gulf of Aden since the first wave of US-UK strikes.
But the prime minister insisted the latest British military action had worked to “degrade capability”, though noted there “may be a difference between reducing and eliminating” the threat.
“The targets are specifically selected on the basis of intelligence, military sites which impact the security and safety of seafarers and shipping, and to that end I’m confident the strikes are being carried out in a way that’s effective and achieving their aim,” he told MPs.
Mr Sunak said action against the Houthis had been a “last resort” and only after repeated warnings had been ignored, adding that the UK in both waves of attacks had acted in order to “protect innocent lives and preserve the freedom of navigation”.
The government’s aim is to stop the illegal sale of weapons to the Houthis and impose sanctions to cut off the group’s financial resources, he added.
The government has published the legal advice it received for the operation, which concluded the strikes were legal under international law.
Sir Keir Starmer backed the strikes and said attacks on vessels needed to stop.
“They are designed to destabilise us so we must stand united and strong, they bring danger to ordinary civilians who are working hard at sea, so we must protect them, and they aim to disrupt the flow of goods, food and medicines, so we must not let them go unaddressed,” he said.
A “general debate” on military action in the region will take place in the Commons on Wednesday. MPs will not be asked to consider and vote on a specific motion.
Liberal Democrat leader Sir Ed Davey, who has called for a vote, said his party accepted the case for the strikes but that there had been “remarkably little clarity about what the next steps are and when the UK’s objectives will be judged to have been fulfilled”.
Downing Street has defended the decision not to consult Parliament first, arguing that the government was “acting with precedent” and that “there isn’t a requirement to hold a vote”.
Meanwhile, Foreign Secretary Lord Cameron will be visiting the region this week.