In a statement, the rights monitor said the Sudan Shield Forces "intentionally targeted civilians in a January 10 attack" on the village of Tayba in Al-Jazira state, where fighting between the army and its rival the paramilitary Rapid Support Forces (RSF) has intensified in recent weeks.

Tayba is located 30 kilometres (12 miles) east of state capital Wad Madani, which the army recaptured from the RSF last month after more than a year of paramilitary control.

The attack, Human Rights Watch (HRW) said, left at least 26 civilians dead, one of them a child, and saw the systematic looting of property, including food supplies, as well as the burning of houses.

"These acts constitute war crimes and some, such as the deliberate killings of civilians, may also constitute potential crimes against humanity," it added.

The Sudan Shield Forces are led by Abu Aqla Kaykal, who defected from the RSF last year and has been accused of atrocities against civilians both during his tenure with the paramilitaries and now on the army's side.

Since April 2023, the conflict in Sudan has pitted army chief Abdel Fattah al-Burhan against his former deputy, RSF leader Mohamed Hamdan Daglo.

The war has claimed tens of thousands of lives, uprooted more than 12 million people and triggered the world's largest displacement and hunger crisis.

- 'You slave' -

Both the army and the RSF have been accused of grave atrocities against civilians, with their leaders sanctioned by the United States.

HRW's investigation, based on survivor testimonies, satellite imagery, and verified videos and photos, documented widespread destruction and extrajudicial killings.

It said that the communities in Tayba were targeted twice on January 10.

Tayba, whose residents identified Kaykal's fighters as members of Sudan's ethnic Arab majority, is home to communities of non-Arab ethnic groups originally from western Sudan called Kanabi.

Some survivors reported hearing racial slurs shouted during the attack, such as "You slave!".

"'Do you not know who Kaykal's troops are? Do you not know who we are?'" one woman recalled the fighters saying.

"The Sudanese authorities should urgently investigate all reported abuses and hold to account those responsible, including the commanders of the Sudan Shield Forces," said Jean-Baptiste Gallopin, senior crisis, conflict and arms researcher at HRW.

In a statement after the attack, the army denied any involvement, attributing it to "individual violations" and pledged to hold perpetrators accountable.

Though the RSF has become notorious for alleged ethnicity-based violence -- leading the US last month to accuse it of genocide -- reports have also emerged of civilians being targeted on the basis of ethnicity in army-controlled areas.