The crisis facing Sudan's president Omar al-Bashir deepened on Tuesday evening after the country's police force said it would no-longer intervene against demonstrators demanding his resignation and called for a "peaceful transition of power."

The statement by the police follows three nights of massive demonstrations in the capital city that have seen army officers stepping in to fight off security forces trying to clear protester off the streets, and suggests divisions within the regime and its security services are widening.

Hundreds of thousands of people chanting "freedom" have rallied outside Sudan's army headquarters in central Khartoum since Saturday. The sit-in is the biggest rally since protests demanding Mr Bashir's resignation began in December.

The demonstrators, who are led by a loose alliance of trade unions called the Sudan Professionals Association, have called on the army to protect them from the National Intelligence and Security Service (NIISA) and riot police who have tried to clear the area several times.