Who are the Rapid Support Forces?published at 12:52 British Summer Time 17 April 2023
The RSF, as it's commonly referred to, was formed in 2013 and has its origins in the notorious Janjaweed militia - which brutally fought off rebels in Darfur.
Since then its leader Gen Mohamed Hamdan Dagalo has built a powerful force that has intervened in conflicts in Yemen and Libya, and controls some of Sudan's gold mines.
It has also been accused of human rights abuses, including the massacre of more than 120 protesters in June 2019.
Such a strong force outside the army has been seen as a source of instability in the country.
Find out more about the military rivalry behind the clashes in Khartoum here.