The United States and United Nations have warned the situation in Sudan's region of West Darfur could herald a repeat of past mass atrocities there as fighting in the restive nation reached its third month.
The fighting between Sudan's army and the paramilitary Rapid Support Forces broke out on April 15 but quickly spread westward, hitting cities in the Kordofan and Darfur regions.
"Darfur is rapidly spiralling into a humanitarian calamity. The world cannot allow this to happen. Not again," the UN aid chief Martin Griffiths said in a statement on Thursday.
Activists said El Geneina, on the border with Chad, has been particularly badly hit. Fighting has killed 1,100 people and sent more 270,000 refugees across the border to Chad. Homes and hospitals have been destroyed.
The United States blamed the Rapid Support Forces and allied militias for the violence. But army aircraft and drone attacks had impeded humanitarian efforts, it said.
The situation there was "an ominous reminder of the horrific events that led the United States to determine in 2004 that genocide had been committed in Darfur," the US State Department said in a statement.
Unrest rooted in 2000s
In the early 2000s, Sudan's army relied on Arab militias to put down a rebellion by armed Darfuri groups. Those militias, known as the Janjaweed, formed the origin of the Rapid Support Forces, which evolved into a force that was legalised in 2017.
Then-president Omar al-Bashir and aides are wanted by the International Criminal Court for genocide and crimes against humanity after 300,000 people were killed and millions displaced.
A letter from several US and Sudanese activist and civil society groups called on RSF commanders to be held accountable for failing to rein in their soldiers and for the army to be held accountable for not protecting civilians.
The US statement said army aircraft and drone attacks had impeded humanitarian efforts.
The UN refugee agency also expressed concern, citing reports of "shocking incidents of sexual violence," including by fighters entering civilian homes and stopping them at checkpoints as they tried to flee conflict zones.
Human trafficking, particularly in East Sudan, was on the rise, it said.
Children at risk
The conflict in Sudan has displaced more than one million children, 270,000 of them in the Darfur region, the UN children's agency (UNICEF) has said, warning "many more are at grave risk".
As well as the more than one million displaced, at least 330 children have been killed and more than 1,900 wounded, UNICEF said in a statement on Thursday.
The United Nations agency said an estimated 13 million children were in "dire need" of humanitarian assistance.
"Children are trapped in an unrelenting nightmare, bearing the heaviest burden of a violent crisis they had no hand in creating -- caught in the crossfire, injured, abused, displaced and subjected to disease and malnutrition," said UNICEF Sudan representative Mandeep O'Brien.
"All those responsible for this killing must be held to account including those who bear command responsibility," Jeremy Laurence, spokesperson for the UN rights office, told reporters in Geneva.