Sudanese police fired tear gas at hundreds of protesters who tried to march on parliament Sunday, as President Omar al-Bashir insisted demonstrators who died in anti-government rallies were not killed by security forces. Deadly protests which erupted on December 19 after a government decision to triple the price of bread have turned into nationwide rallies against Bashir's three decades of iron-fisted rule. On Sunday, as the protest movement entered its second month, hundreds of demonstrators attempted to march on parliament in Omdurman, the twin city of Khartoum, but they were quickly confronted by riot police who fired tear gas, witnesses said. Protesters then staged simultaneous rallies in different neighbourhoods of Omdurman in an attempt to gather again for the march, a witness said, but they were unable to. They shouted "freedom, peace and justice", the main slogan of the protest movement, and "overthrow, overthrow", the witness said. Late on Sunday residents of Omdurman continued to protest in three areas, according to the Sudanese Professionals Association (SPA), which is leading the protest movement. "Some protesters have fainted from the tear gas, while some are wounded," it added, without elaborating. Protesters in Omdurman had planned to march on parliament to submit a "memorandum to lawmakers" calling for Bashir's resignation, said the SPA, which represents several unions of doctors, engineers and teachers. Witnesses said protests were also staged in the capital's eastern district of Burri -- the site of heavy clashes on Thursday -- and in the northern suburb of Bahari. - 'Killers among demonstrators' - Protests were also held in some areas in the central town of Madani, witnesses said. Officials say 26 people, including two security personnel, have died in the protests so far, while rights group Amnesty International has put the death toll at more than 40. The protests have emerged as the biggest challenge yet to the authority of President Bashir, who swept to power in 1989 in an Islamist-backed coup. They come as Sudan suffers from an economic crisis driven by an acute shortage of foreign currency and soaring inflation that has more than doubled the price of food and medicines. Riot police and Sudan's feared National Intelligence and Security Service (NISS) have led a sweeping crackdown on the protest movement that has seen several opposition leaders, activists, journalists and protesters jailed since the demonstrations erupted. The government's tough response has sparked international criticism, with Amnesty International accusing the security forces of using violence against protesters. Bashir rejected the accusations on Sunday at a rally in Al-Kurreida village in the White Nile state, alleging that groups within the protest movement were behind the killing of demonstrators. "There are some people among the protesters who are killing the demonstrators," Bashir said in a speech broadcast live on state television, without specifying who the culprits were. He said a doctor who died on Thursday in Burri was not killed by security forces. "The doctor who was killed in Burri was killed by a weapon that did not belong to the army, or NISS, or police," said Bashir, dressed in a traditional white robe and turban. "He was killed by someone from among the demonstrators." - 'All towns and cities' - On Thursday, Khartoum was rocked by several demonstrations, including one in Burri that saw clashes between riot police and protesters. Later, a doctors' committee linked to the SPA had said the doctor was killed by live ammunition but did not specify who had fired the shots. Sarah Jackson, Amnesty's deputy director for East Africa, said Friday it was an "outrage that Sudanese security forces continue to use lethal force on protesters and key service providers like doctors". She accused security personnel of "killing people in an unbridled spree". Amnesty has reported repeated raids on medical facilities by the security forces, saying they have fired tear gas and live bullets inside hospitals as well as arresting and beating doctors. The SPA said there would be night-time demonstrations on Tuesday in the capital and in Omdurman. More rallies were planned for Thursday "across all towns and cities of Sudan," the group said.