The United Nations said Friday it was "alarmed" at death sentences given by a court run by Yemen's Huthi rebels to 30 academics, trade unionists and preachers for alleged spying.

"The UN Human Rights Office has received credible information suggesting that many of those convicted were subjected to arbitrary or unlawful detention, as well as torture," rights office spokeswoman Ravina Shamdasani told reporters.

Those condemned were accused of spying for the Saudi-led coalition, which intervened in Yemen in March 2015, shortly after the Iran-backed Huthis seized the capital Sanaa.

Shamdasani noted the group will likely appeal to a higher court, which is also under Huthi control.

The rights office urged the appeals court to consider "the serious allegations of torture and other ill-treatment, and of violations of the fair trial and due process rights of the convicted people," Shamdasani said.

The Huthis have been accused by rights groups of using Sanaa's courts to target opponents and critics.

Yemen's conflict has killed tens of thousands of people, many of them civilians, relief agencies say, and left millions displaced and in need of aid.AFP