By Khalid Abdelaziz and Ulf Laessing
KHARTOUM, Sept 27 (Reuters) - Sudanese security forces have killed at least 50 protesters with shots to the head or chest, two rights groups said on Friday, challenging the authorities' narrative of the worst unrest in Sudan's central regions for years.
Spurred on by the lifting of fuel subsidies on Monday, thousands of people have taken to the streets in Khartoum and central Sudan to protest against corruption and demand veteran President Omar Hassan Bashir step down.
Sudan's police, which has cracked down on the protests, said late on Thursday that battles with protesters had killed 29 people, among them police officers. Sudanese opposition activists have put the death toll at over 100.
London-based Amnesty International and the New York-based African Center for Justice and Peace Studies said at least 50 people had been killed by gun shots to the chest or head, citing witnesses, relatives, doctors and journalists.
Among the dead was a 14-year-old boy, while most other victims seemed to be between 19 and 26 years old, the groups said in a statement. Hundreds had been detained, it said.
"Shooting to kill - including by aiming at protesters' chests and heads - is a blatant violation of the right to life, and Sudan must immediately end this violent repression by its security forces," said Lucy Freeman, Africa Deputy Director at Amnesty International.
Sudanese officials could not be immediately reached for comment but Information Minister Ahmed Belal Osman said late on Thursday any figures higher than 29 were inaccurate.
New York-based Human Rights Watch (HRW) said in a separate statement it had confirmed that the death toll was higher than the official 29. It did not give a number.
"The police and national security forces fired teargas, rubber bullets, and according to credible reports, live ammunition into the crowds," HRW said.
It was not immediately possible to verify the allegations.
Reuters footage from a protest in Khartoum on Wednesday showed protesters holding up rifle cartridges at a time. Correspondents saw dozens of plain-clothes agents carrying guns.
Activists have called for more protests after Friday prayers. Trucks with mounted machine or anti-aircraft guns, usually only used in strife-torn regions such as Darfur in Sudan's west, were parked at main roads and near large mosques across Khartoum and its twin-city Omdurman at the Nile confluence.
Sudan's divided and weak opposition has tried several times to bring to Sudan an "Arab spring" unseating rulers in the region but has failed to mobilise masses seen in Egypt or Libya.
Bashir still enjoys support from the army, security apparatus, his ruling party and wealthy Sudanese with extensive business interests. (Reporting by Ulf Laessing; Editing by Elizabeth Piper)