Nairobi/Khartoum: Amnesty International said it has received "credible reports" that Sudanese security forces have shot dead 37 protesters in a crackdown on demonstrations roiling the country.
Anti-government protests have rattled Sudan since Wednesday after the government tripled the price of a loaf of bread.
The authorities say eight protesters have been killed in the unrest, while Sudan's main opposition leader Sadiq Al Mahdi on Saturday put the death toll at 22.
The rights group said in a statement late Monday it "has credible reports that 37 protesters have been shot dead by the security forces in five days of anti-government demonstrations".
"The fact that the security forces are using lethal force so indiscriminately against unarmed protesters is extremely troubling," said Sarah Jackson, Amnesty's director for East Africa, the Great Lakes and the Horn.
"With dozens already dead, the government must rein in this deadly use of force and prevent more unnecessary bloodshed."
There was no immediate Sudanese government reaction to the Amnesty statement.
Demonstrations have hit a dozen cities across the economically troubled country since the bread price hike last week.
Sudan President Omar Al Bashir vowed "real reforms" on Monday after days of deadly protest which pose one of the biggest challenges he has faced during decades in power.
As demonstrations sparked by a hike in bread prices entered their sixth day, doctors went on strike in a country beset by economic woes.
Bashir responded by vowing to "take real reforms to guarantee a decent life for citizens," in quotes carried by the official SUNA news agency.
The president's pledge comes after the protest movement spread to around a dozen cities since it began on Wednesday, after the government tripled the price of bread.
Hospital workers were the first to take part in the doctors' walkout on Monday morning, according to Mohammed Al Assam, a member of a committee of doctors.
The committee said 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 walkout comes after a gathering of professionals from various sectors issued a call on Sunday to strike, as protests hit cities -- including Omdurman, close to the capital Khartoum -- late into the evening.
As the demonstrations continued on Monday, rallies erupted in two cities in Gezira state, south of Khartoum, which Bashir is expected to visit on Tuesday, according to SUNA.
Residents of Manaqil and Rufaa cities told AFP by phone that dozens took to the streets in Manaqil, calling for the fall of Bashir's regime. In Rufaa, protesters blocked the streets and burned tyres.
Witnesses said police armed with batons dispersed the protests.
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, SUNA reported on Sunday.
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, Sudan has grappled with inflation of more than 70 per cent and a plunge in the value of the 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 said.
The ruling National Congress Party has said it understands the population's anger over the economic situation.