In its first report, the Commission of Human Rights Experts on Ethiopia said it had found evidence of a wide range of violations in the country by all sides since fighting erupted in the northern Tigray region in November 2020.
The commission, created by the UN Human Rights Council last year and made up of three independent rights experts, said it had "reasonable grounds to believe that, in several instances, these violations amount to war crimes and crimes against humanity".
The experts highlighted the horrifying situation in Tigray, where the government and its allies have denied around six million people access to basic services, including the internet and banking, for over a year, and where severe restrictions on humanitarian access have left 90 percent of the population in dire need of assistance.
The report said there were "reasonable grounds to believe that the Federal Government and allied regional State governments have committed and continue to commit the crimes against humanity of persecution on ethnic grounds and other inhumane acts."
They were "intentionally causing great suffering or serious injury to body or to mental or physical health based on their ongoing denial and obstruction of humanitarian assistance to Tigray," the report said.
In a statement, commission chair Kaari Betty Murungi described the humanitarian crisis in Tigray as "shocking, both in terms of scale and duration."
"The widespread denial and obstruction of access to basic services, food, healthcare, and humanitarian assistance is having a devastating impact on the civilian population, and we have reasonable grounds to believe it amounts to a crime against humanity," she said.
"We also have reasonable grounds to believe that the Federal Government is using starvation as a method of warfare," she added, calling on the government to "immediately restore basic services and ensure full and unfettered humanitarian access."
Murungi also called on Tigrayan forces to "ensure that humanitarian agencies are able to operate without impediment."
Tigray has been bombed several times since fighting resumed in late August between government forces and their allies, and rebels led by the TPLF, which ruled Ethiopia for decades before Abiy took office in 2018.
The return to combat shattered a March truce and dashed hopes of peacefully resolving the war, which has killed untold numbers of civilians and triggered a humanitarian crisis in northern Ethiopia.
"With a resumption of hostilities in northern Ethiopia, there is a very real risk of further civilian suffering and further atrocity crimes," Murungi warned.
"The international community should not turn a blind eye, and instead increase efforts to secure a cessation of hostilities and the restoration of humanitarian aid and services to Tigray," she said.
"Failure to do so would be catastrophic for the Ethiopian people, and has wider implications for peace and stability in the region."