The latest victim, a little girl, succumbed to her injuries Monday. Her four year-old brother and a woman were also killed when a grenade detonated near an anti-government protest site.
The blast injured at least twenty-two others, including a nine-year-old boy.
Earlier Sunday, a gunman killed a five-year-old girl when he opened fire at an anti-government protest in eastern Thailand.
The embattled Prime Minister, Yingluck Shinawatra has condemned the violence, calling them "terrorist acts for political gain."
Protesters have been calling for her resignation. The army, according to the BBC, is sympathetic to the protesters.
On Monday, Army Chief Prayuth Chan-ocha shot down speculation the army might intervene. In a televised address, he said: "Somebody has to take responsibility but that doesn't mean soldiers can intervene without working under the framework [of the law]. ... How can we be sure that if we use soldiers, the situation will return to peace?"
Anti-government protests, led by the opposition Democrat Party, have been ongoing since November 2013. Protesters are calling for the removal of the Prime Minister Yingluck Shinawatra, whom they accuse of acting on behalf of her brother, ousted former Prime Minister Thaksin Shinawatra.