The UN on Sunday condemned Yemeni rebels' execution of nine people for their alleged involvement in the killing of a top Houthi leader.

The Iran-backed Houthis are battling the Yemeni government -- which is supported by a Saudi-led military coalition -- for control of the impoverished country.

The rebels said they executed the nine individuals on Saturday for their involvement in the killing of Saleh al-Sammad, who was head of the Houthis' supreme political council, in a 2018 air strike claimed by Saudi Arabia.

They were among 16 people convicted by a Huthi court.

United Nations Secretary-General Antonio Guterres "deeply regrets" the executions, spokesman Stephane Dujarric said in a statement, adding that one of the people was reportedly a minor at time of detention.

Guterres "strongly condemns these actions which are a result of judicial proceedings that do not appear to have fulfilled the requirements of fair trial and due process under international law," the statement added.

Dujarric said Guterres was also concerned about a reported coalition air strike this week in the southern province of Shabwa "that allegedly killed at least six civilians from the same family".

A local pro-government official who spoke on condition of anonymity told AFP that at least five civilians, including three women, were "accidentally" killed in an air strike on Saturday while they were travelling in their car.

The Saudi-led military coalition could not be immediately reached for comment.

Yemen's conflict began in 2014 when the Houthis seized the capital Sanaa, prompting the Saudi-led coalition to intervene the following year.

Since then, tens of thousands have been killed and millions pushed to the brink of famine in what the UN calls the world's worst humanitarian crisis.