The United States on Tuesday imposed sanctions on two commanders of Yemen's Huthi rebels, blaming them for civilian deaths and denouncing their ties with Iran as Washington seeks to halt the devastating war.

The Treasury Department said it would freeze any assets of the air force and naval commanders of the Huthis, who have defied international appeals by pursuing an offensive to seize the government's last northern stronghold.

With the rebels from the impoverished nation unlikely to have US bank accounts, the effects are largely symbolic but reinforce President Joe Biden's sharp criticism of Iran even as he opens the door to diplomacy and distances his administration from Saudi Arabia, which has been waging a devastating campaign to dislodge the Huthis.

"These individuals command forces that are worsening the humanitarian crisis in Yemen," said Andrea Gacki, the director of the Treasury Department's Office of Foreign Assets Control.

"The United States remains committed to promoting accountability of Huthi leadership for their actions, which have contributed to the extraordinary suffering of the Yemeni people," she said in a statement.

The Treasury Department said that both commanders had trained in Iran and acquired weapons from the clerical state, which has religious affinities with the Huthis and a shared hostility toward Saudi Arabia.

The Huthi naval commander, Mansur al-Saadi, masterminded deadly attacks against international shipping in the Red Sea and put fishermen and other civilians at risk with naval mines, the Treasury Department said.

The air force commander, Ahmad Ali Ahsan al-Hamzi, has carried out targeted drone strikes, it said.

The action comes after the Biden administration in one of its first acts rescinded a designation that the Huthis, formally known as Ansar Allah, are a terrorist organization.

Aid groups said that the label put their work at risk as they had no choice but to deal with the Huthis, who effectively are Yemen's governing authority in much of the country including the capital Sanaa.

Former president Donald Trump's administration, which fiercely opposed Iran and was closely aligned with Saudi Arabia, had branded the Huthis as terrorists in its final days in office.

The United Nations has called Yemen the world's worst humanitarian crisis and voiced disappointment after a pledging conference Monday raised $1.7 billion in aid, far below the appeal of $3.85 billion.