The British government would not "hesitate to protect" UK security amid ongoing tensions with Houthi rebels, Rishi Sunak has said.
The British military joined forces with the US on Thursday night as it launched attacks against Houthi bases in Yemen - in retaliation for the targeting of international trade in the Red Sea.
The prime minister said the aim of the action was to "de-escalate tensions in the region and actually restore stability back to the area".
However, with questions swirling around over whether further action would be taken, he added the UK "will not hesitate to protect our security where required".
Mr Sunak is due to give a statement in the Commons about the operation at around 3.30pm.
The US carried out a further strike in Yemen on Friday, but reports suggest only 25% of the Houthi capability to carry out attacks on cargo ships had been damaged.
Earlier, Defence Secretary Grant Shapps told Sky News: "We never thought that this would remove all of their facilities. That wasn't the goal. The goal was to send a very clear message."
Describing Houthi attacks on the key shipping lane as "thuggery", Mr Shapps also said there was no planned escalation of the action, and the UK's "intention" was not to go into Yemen.
But he insisted the government would "monitor the situation very carefully".
A spokesman for the Yemeni armed forces in the Houthi-controlled north of the country said in a televised statement the bombardment would "not go unanswered and unpunished".
And it linked the strikes with the ongoing war between Israel and Hamas, saying it would not deter their support for the Palestinians.
On Sunday, Foreign Secretary Lord Cameron denied any link between the Yemen strikes and the war in Gaza to Sky News, saying the action was "completely separate".
But experts warned those in Arab nations would be unlikely to see it in the same way.
Speaking to reporters on Monday, Mr Sunak said: "We faced an escalating series of attacks from the Houthis on commercial shipping, including an attack on a Royal Navy warship. That's unacceptable.
"It's right that we took proportionate, targeted action against military targets to send a strong message that that behaviour is unacceptable.
"It was a last resort, it came after the end of exhaustive diplomatic activity including a UN Security Council."
The prime minister added: "Now, I think it is incumbent on the Houthis to recognise the international condemnation for what they are doing and desist.
"But we, of course, will not hesitate to protect our security where required."
Mr Sunak will make a statement on the military action in the Commons later on Monday, four days after the strikes.
He briefed Labour leader Sir Keir Starmer ahead of the strikes on Thursday, as well as the Speaker, Sir Lindsay Hoyle.
Speaking to reporters on Monday, Sir Keir said: "The action that the government took in conjunction with the US is action that we support.
"What we now need to hear from the prime minister is the scope, the basis, the full reasoning behind the decision that he took and of course the question of whether more action may be needed, and what processes will be put in place."
However, some MPs are angry ministers did not bring the issue to parliament before joining the US-led operation last week, with the Liberal Democrats demanding a retrospective vote on the issue.
Asked if he would support further strikes in Yemen, Sir Keir said: "If the government is proposing further action, then it should say so and set out the case and we're going to have to consider that on a case by case basis on the merits."