Doctors in Sudan went on strike on Monday, feeding into deadly protests against bread prices that represent one of the biggest challenges President Omar al-Bashir has faced in nearly three decades in power.A gathering of professionals from various sectors had issued a call on Sunday to strike as fresh protests hit cities - including Omdurman, close to the capital Khartoum - late into the evening.The strike "started at 0600 GMT in the morning" and hospital workers were the first to take part, said Mohammed al-Assam, a member of a committee of doctors.The committee said in a statement that it would submit an official demand on Tuesday for the "president's immediate resignation in response to the uprising by the Sudanese people... (and the) formation of a transitional government". The protest movement has hit around a dozen cities since on Wednesday, after the government tripled the price of bread, in a country beset by economic crisis.Eight people have died in demonstrations in the eastern cities of Al-Gadaref and Atbara during clashes with security forces, according to officials and witnesses. But others have spoken of higher death tolls. Opposition leader Sadiq al-Mahdi said on Saturday that 22 people had died, denouncing what he called "armed repression" against a legitimate protest movement. 'Political roots' Mahdi, Sudan's last democratically elected prime minister, was overthrown in a coup that brought Bashir to power in 1989.Pushed into exile several times, Mahdi returned to his homeland on Wednesday, the day protests began. After initially railing against the high cost of living, some protesters have also adopted the slogan used in the 2011 Arab Spring - "the people want the fall of the regime". Mahdi has likewise called for the government to go."The main reason for the protests is economic and linked to high prices but the roots of the economic crisis are political", according to Abdellattif al-Bouni, a political science professor. "The political failures of the government, errors and bad management" explain why people are so angry, he said. In January, protests erupted against the high price of basic foodstuffs, but were quickly quelled by the authorities, which arrested opposition leaders and militants. Several opposition party members -- accused of vandalism during the ongoing protests -- have been arrested, the official Suna news agency said on Sunday. Reforms For Mohamed Lattif, a political columnist for the Al-Youm Al-Tali newspaper, scarce state resources and the entrenched economic crisis must now result in political reform. When South Sudan seceded to become the world's newest country in 2011, Sudan lost three quarters of its oil reserves.This year, the country has grappled with inflation of more than 70% and a plunge in the value of the Sudanese pound against the dollar."There is no choice but to look again at the leadership structure," Lattif said. What comes after the protests depends on the government, he said."If they persist with a security response... we will also see an escalation by the other side", he predicted. Indicted by the International Criminal Court for crimes against humanity, war crimes and genocide in Sudan's western Darfur provinces, Bashir is seen by experts as an authoritarian and volatile leader.The ruling National Congress Party has said it understands the population's anger over the economic situation. But spokesman Ibrahim el-Sadik also accuses Israel of being behind the protests, alongside "left-wing parties that hope to destabilise the state". Sudan's government, like others in the region, often says interference by foreign powers - particularly the US and Israel - guides domestic unrest.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.