President Omar al-Bashir on Saturday accused Amnesty International of spreading "lies" that Sudanese government forces had used chemical weapons against civilians in war-torn Darfur.
Last month, Amnesty said in a report that Sudanese forces had carried out more than 30 suspected chemical weapons attacks in a mountainous area of Darfur that killed up to 250 people, including many children.
"In the past few days you have been following all the lies and allegations made by Amnesty International about use of chemical weapons," Bashir said in an address to workers of his National Congress Party.
"These are just empty lies," Bashir said in his first reaction to Amnesty`s report.
The rights group accused Sudanese forces of "the repeated use" of suspected chemical weapons against civilians in Darfur`s remote and thickly forested Jebel Marra area between January and September.
"Between 200 and 250 people may have died as a result of exposure to the chemical weapons agents, with many or most being children," Amnesty said.
The nearly 100-page report contained gruesome photographs of children suffering from apparent chemical burns, satellite images of destroyed villages and displaced people, interviews with more than 200 survivors and analysis by chemical weapons experts.
Amnesty said the attacks were part of a military operation against the rebel Sudan Liberation Army - Abdul Wahid (SLA/AW) group, which Khartoum accuses of ambushing military convoys and attacking civilians.
Tens of thousands of people have been displaced in Jebel Marra since mid-January by fighting between the two sides, the United Nations says.
The UN has urged Sudan to shed light on Amnesty`s claims, while the Organisation for the Prohibition of Chemical Weapons (OPCW) has sought further evidence to push for a formal investigation.
Sudan is a signatory to the Chemical Weapons Convention.
Darfur has been engulfed in a deadly conflict since 2003 when ethnic minority groups took up arms against Bashir`s Arab-dominated government, which launched a brutal counter-insurgency.
At least 300,000 people have been killed and 2.5 million displaced in Darfur since then, the UN says.
Bashir is wanted by the International Criminal Court on war crimes and genocide charges related to Darfur, which he denies.
Sudan insists that the conflict in Darfur has ended, and that it wants UN peacekeepers who have been deployed in the region the size of France since 2007 to leave.