Two people were killed in the Saturday attack in the northern city of Arusha at a large rally of the main opposition Chadema party on Saturday evening led by its president Freeman Mbowe, while some 60 more were wounded.
A third person died from their wounds on Monday, said Josiah Mlay, chief doctor in Arusha’s main hospital.
Tanzanian police chief Saidi Mwema said officers were investigating the attack, which he said was a “suspected act of terrorism.”
There was no claim of responsibility for the attack, which took place on the last day of campaigning for municipal council elections.
Samson Mwigamba, Chadema’s official in Arusha, said the attack was “politically motivated” and the party’s leader “narrowly escaped death.”
President Jakaya Kikwete condemned the attack, saying it was carried out by those wanting to “cultivate hatred” among citizens.
Last month attackers wounded 30 when they hurled an improvised bomb into a Catholic church in Arusha, a town popular with tourists visiting the nearby Serengeti national park and snowcapped Mount Kilimanjaro, but there was no indication the attacks were linked.
In the national assembly, Chadema — or Chama cha Demokrasia na Maendeleo, meaning in Swahili, the Party for Democracy and Progress — holds just under a fifth of seats.