The United Nations High Commissioner for Human Rights is "deeply concerned" about the human rights situation in Yemen, where all parties to the conflict are "violating" international human rights law.
"Civilians across the country are paying a heavy price, while armed groups control territory and exercise power in complete disregard for human rights and international humanitarian law," OHCHR spokeswoman, Marta Hurtado, said in a statement.
The statement noted the Houthi rebels' execution of nine Yemenis on September 18, including one who allegedly had been a minor at the time of his arrest.
"The defendants had been sentenced to death in a judicial process that violated their constitutional rights, and did not respect fair trial standards under international law", the statement said.
The statement has also pointed to the repeated use of drones and missile attacks by the Houthis and the Saudi-led coalition, which "have resulted in civilian casualties and damage or destruction of civilian objects, both in Yemen and the [Saudi] Kingdom."
"Reports that the security forces of the (UAE-backed) Southern Transitional Council authorities used unnecessary and disproportionate force against demonstrators protesting against the deteriorating living conditions and the lack of public services, raise the same level of concern", it added.
The statement stressed that "any attacks against civilian objects or against civilians not taking a direct part in the hostilities may amount to a war crime."
It called on all parties to the conflict to comply with their obligations under international humanitarian law and to conduct investigations with a view to holding those responsible to account for any violations.