Sudan's paramilitaries have declared the formation of a rival government to the country's armed forces, two years into a war that has become the world's largest humanitarian crisis.

The leader of the Rapid Support Forces (RSF), Mohamed Hamdan "Hemedti" Dagalo, said the group was "building the only realistic future for Sudan".

The announcement came as London hosted an high-level conference to mark the second anniversary of the conflict, where the UK Foreign Secretary David Lammy called for "a pathway to peace".

Fighting raged on, with the army saying it had bombed RSF positions outside the city of el-Fasher, forcing hundreds of thousands to flee the Zamzam refugee camp.

Hemedti said the RSF was building a "state of law" and not a state ruled by individuals.

"We do not seek domination, but unity. We believe that no tribe, region, or religion holds a monopoly over Sudanese identity," his statement on Telegram read.

He added that his government would provide essential services such as education and healthcare to not only RSF-controlled areas, but the whole country.

More than 400 people have been killed in recent attacks by the RSF, according to the UN, citing "credible sources".

Two years into the war, both the army and RSF have been accused of war crimes, including genocide and mass sexual violence.

Hemedti has been locked in a power struggle with Sudan's army chief, Gen Abdel Fattah al-Burhan, since 15 April 2023, creating a humanitarian crisis that has claimed more than 150,000 lives and displaced more than 12 million people.

The latest fighting in the capital of North Darfur, el-Fasher, has forced tens of thousands of civilians from the Zamzam refugee camp to walk 70km (43 miles) to the town of Tawila, according to medical charity MSF.

Many arrived severely dehydrated and some children are reported to have died of thirst.

Humanitarian agencies have reported famine-like conditions facing more than 700,000 people in temporary camps around el-Fasher, with security threats and roadblocks thwarting the delivery of critical aid.

During an international meeting on Tuesday, the UK promised an extra £120m ($159m) worth of food and medical assistance, urging the world not to turn its back on Sudan.

"Many have given up on Sudan – that is wrong – it's morally wrong when we see so many civilians beheaded, infants as young as one subjected to sexual violence, more people facing famine than anywhere else in the world... We simply cannot look away," Lammy said.

The conference also called for an immediate and permanent ceasefire, but the African Union has said it will not allow the country to be partitioned by the army and the RSF.