(AFP) - Ethiopian forces shelled heavily populated areas in the first weeks of the conflict in the Tigray region, killing at least 83 civilians and displacing thousands, Human Rights Watch said Thursday.

Artillery attacks by forces backing Prime Minister Abiy Ahmed, the 2019 Nobel Peace Prize winner, "struck homes, hospitals, schools and markets", according to the report, which focuses on the regional capital Mekele and the towns of Shire and Humera.

"At the war's start, Ethiopian federal forces fired artillery into Tigray's urban areas in an apparently indiscriminate manner that was bound to cause civilian casualties and property damage," said Laetitia Bader, HRW's Horn of Africa director.

The report calls for a UN investigation of possible laws of war violations.

Abiy announced military operations against the leadership of Tigray's ruling party, the Tigray People's Liberation Front (TPLF), in early November, saying this was in response to TPLF-orchestrated attacks on federal army camps.

He declared victory after pro-government troops took Mekele in late November, though the TPLF vowed to fight on, and aid workers say persistent insecurity has hampered the delivery of badly-needed humanitarian assistance.

Abiy has previously said the military acted with special care for civilian lives, telling lawmakers in late November that no civilians were killed as his forces entered Tigray's cities.

His office did not immediately respond to a request for comment Thursday.

Thousands have died in the conflict in Tigray, according to the International Crisis Group, and tens of thousands of refugees have streamed across the border into Sudan.

- 'We were at a loss' -

In the western town of Humera, doctors reported that at least 46 people were killed and 200 injured on a single day during the first week of fighting, HRW said, adding that "total casualties that day were most likely higher".

"Civilians started arriving in the hospital with injuries to the abdomen, chest, head. We were at a loss," HRW quoted a doctor as saying. "People with no hands, people with their stomachs hanging out."

A doctor at a hospital in Mekele has previously told AFP that 27 civilians were killed in "artillery and rocket shelling" on November 28, the day federal forces arrived, and that more than 100 were wounded.

"Many of the artillery attacks did not appear aimed at specific military targets but struck generalised populated areas," HRW said.

Much of Tigray remains inaccessible to aid workers and the media, making it difficult to get a full picture of the toll of the fighting and current conditions on the ground.

Ethiopia "should promptly allow UN investigators into Tigray to document the conduct by warring parties in a conflict that has devastated the lives of millions and should no longer be ignored," Bader said.

- Aid access -

Fears are growing of a humanitarian catastrophe in Tigray, with the UN warning this week that conditions were "extremely dire" and that "needs have outpaced our capacity to respond."

At a press conference on Wednesday, Abera Tola, head of the Ethiopian Red Cross Society, said that 80 percent of Tigray was "unreachable" and warned that tens of thousands of people could starve to death.

In a statement Thursday, the Red Cross issued a statement specifying that Abera meant the Red Cross did not have "capacity and capability to reach 80 percent of the vulnerable community".

"That is why we are appealing to the public and international community to fill the (gap)," the statement said.

Also on Thursday, the Ethiopian Human Rights Commission, a government-affiliated but independent body, said "ongoing conflict had "impeded the circulation of basic goods, provision of humanitarian assistance and slowed the full resumption of humanitarian aid transport services."

The government says it is working to provide humanitarian assistance to all who need it in Tigray, while expanding access for aid workers as the security situation allows.

© Agence France-Presse