Two American women have been "rescued from captivity" in Yemen's rebel-held capital and flown out of the country in a joint US-Saudi military operation, Saudi officials said on Friday.

The US State Department confirmed it helped the two women get out of Yemen but gave no details, while a rebel official said they had "escaped" but not in a rescue operation.

The young women were "mistreated and had restrictions imposed on their movements" after visiting relatives in Sanaa, which was seized by the Iran-backed Huthi rebels in 2014, according to Riyadh.

"Two young American women were freed from captivity, evacuated, and transported from the Huthi-controlled Yemeni capital Sanaa to the interim capital Aden, and later on to Riyadh," Saudi defence ministry spokesperson Turki al-Malki said in a statement.

The women were evacuated to Riyadh where they were met by US officials and received health checks, the statement said.

In Washington, the State Department said: "We assisted with the safe departure of two US citizens from an area of Yemen currently under Huthi control."

"We express our appreciation to our Saudi and Yemeni government partners for their assistance in facilitating their safe departure. Due to privacy considerations, we have nothing further."

In Sanaa, the interior ministry spokesman of the unrecognised rebel government, Abdul-Khaleq al-Ajri, said the two women had organised their own escape.

Reports of Saudi-US security cooperation were "baseless", he said in a statement published by rebel media.

He gave their names as sisters Zahraa and Samiha Amin Abdul Karim Sufyan, who last month had married two brothers seeking American nationality in return for a "dowry" of $61,000.

The women had coordinated their escape "with two men who transported them to Aden" in government-held southern Yemen, he said, without specifying if they were of Yemeni origin.

Yemen, the Arab world's poorest country, is wracked by war between the Huthis and a Saudi-led coalition fighting on behalf of the internationally recognised government.

In February, Washington slapped sanctions on members of an international network for funding the rebels.

The Huthis have stepped up cross-border attacks on Saudi Arabia and in January claimed their first deadly assault on the United Arab Emirates.

47 children killed, maimed

Forty-seven children were "killed or maimed" in Yemen's civil war in January and February following a surge in violence, the United Nations children's fund said on Saturday.

Children are the "first and most to suffer", UNICEF said, adding that a total of at least over 10,000 minors have been killed or injured in a war that has raged since 2015.

"Just over the first two months of this year, 47 children were reportedly killed or maimed in several locations across Yemen," Philippe Duamelle, UNICEF representative to Yemen, said in a statement.

"Since the conflict escalated in Yemen nearly seven years ago, the UN verified that more than 10,200 children have been killed or injured. The actual number is likely much higher."

In the Ukraine war, at least 71 children have been killed and more than 100 wounded in two weeks since Russia's invasion on February 24, a Ukrainian parliament official said Thursday.

Hundreds of thousands of people have died as a direct or indirect consequence of Yemen's war between Iran-backed Huthi rebels and a government forces backed by a Saudi-led military coalition.

In November, the UN Development Programme said 377,000 lives would have been lost through fighting, hunger, unclean water and disease by the end of 2021.

"Violence, misery and grief have been commonplace in Yemen with severe consequences on millions of children and families," Duamelle said.

"It is high time that a sustainable political solution is reached for people and their children to finally live in the peace they so well deserve."

The conflict has caused a collapse in basic services such as healthcare and education, with millions of people displaced and 80 percent of the population dependent on aid.

More than 2,500 schools are unusable, according to UNICEF, as they have been destroyed, converted for military purposes, or used to shelter the displaced. 

A report released by the UN Security Council in January said nearly 2,000 children recruited by the rebels had died on the battlefield between January 2020 and May 2021.