The international community voiced concern as the United States and the Houthi group have both vowed escalation after US President Donald Trump ordered his first airstrikes in Yemen, which killed 53 people, including five children.

The Houthis claimed on Monday to have twice attacked a US aircraft carrier group within 24 hours, calling it retaliation for Saturday's US strikes. According to a US official, the Houthis did fire drones and at least one missile in response to the US attack.

China on Monday called for a dialogue and de-escalation of tensions in the Red Sea.

"China opposes any action that escalates the situation in the Red Sea," Foreign Ministry spokeswoman Mao Ning told a news conference in Beijing. "The reasons behind the situation in the Red Sea and the Yemen issue are complex and should be properly resolved through dialogue and negotiation."

In a statement, United Nations Secretary-General Antonio Guterres called for "utmost restraint and a cessation of all military activities", while warning of "grave risks" to the dire humanitarian situation in Yemen.

"Any additional escalation could exacerbate regional tensions, fuel cycles of retaliation that may further destabilize Yemen and the region, and pose grave risks to the already dire humanitarian situation in the country," his spokesman Stephane Dujarric said.

The warning came after the Houthi Supreme Political Council — the group's highest governing authority — vowed a "painful "retaliation, framing the US attacks as support for Israel and warning they would "drag the situation to a more severe and painful level".

Houthi military spokesman Yahya Sarea initially said they launched 18 missiles and a drone at the "aircraft carrier USS Harry Truman and its accompanying warships" in the Red Sea, hours later claiming to have fired a second round.

In a televised address, Houthi leader Abdulmalik al-Houthi said the US cargo ships would be targeted "as long as it continues its aggression". He called for a million Yemenis to march on Monday in defiance. "If they continue their aggression, we will continue the escalation," he said.

The US airstrikes came days after Houthis said they would resume their attacks against Israeli-linked shipping until the crossings of the Gaza Strip are reopened and aid allowed in.

Washington has vowed to keep striking Yemen until the Houthis stop attacking Israeli-linked Red Sea shipping, with Trump warning he will use "overwhelming lethal force".

US National Security Adviser Mike Waltz told ABC News that Saturday's strikes "targeted multiple Houthi leaders and took them out".Pentagon chief Pete Hegseth vowed an "unrelenting" missile campaign until the Houthi attacks stop.

Updated toll

Saturday's attacks on the capital Sanaa as well as Saada, al-Bayda and Radaa killed 53 people and wounded 98, said Anees al-Asbahi, spokesman for the Houthi-run health authorities, late on Sunday, updating an earlier toll.

Houthi media reported more explosions on Sunday night, accusing the US of targeting a cotton ginning factory in the western region of Hodeida as well as the Galaxy Leader, an Israeli ship captured more than a year ago.

US Secretary of State Marco Rubio told CBS News' Face the Nation program: "There's no way the … Houthis would have the ability to do this kind of thing unless they had support from Iran. And so this was a message to Iran: Don't keep supporting them."

In response, Hossein Salami, the top commander of Iran's Revolutionary Guards, said the Houthis made their own decisions, denying his country was involved. "We warn our enemies that Iran will respond decisively and destructively if they carry out their threats," he told state media.

Given the existing high tensions, these attacks — especially if the US suspects that Iran is continuing to assist the Houthis — will bring Teheran and Washington closer to confrontation, said Danny Citrinowicz, a nonresident fellow with the Atlantic Council's Middle East Programs.

Agencies and Xinhua contributed to this story.