Red Cross officials told Xinhua that the bomb attack hit on Saturday as more than 3 million people gathered in Addis Ababa's Meskel Square to support Ethiopia's Prime Minister Abiy Ahmed.
Some 50 people had received on-site first-aid treatment while some 114 others were taken to healthcare institutions, said the officials.
Prime Minister Ahmed, addressing Ethiopians on TV after the rally, said that a few people were killed and several injured in the blast.
He, however, did not mention the exact number of casualties from the bomb incident.
Ahmed, who affirmed the incident as a prearranged and "carefully orchestrated" attempt to disrupt the peaceful demonstration, also said that investigations are underway to apprehend perpetrators and uncover their motives behind the bomb attack.