All of the blasts took place at around 9 a.m. local time (3:30 a.m. GMT). Both towns in which the explosions took place are several hundred kilometers from the state's main city, Guwahati.
Two bombs went off next to a pond in the center of Gauripur in the Dhubri district, but there were no bystanders.
The other two explosions went off in Bongaigaon while Education Minister Ripun Bora attended an Independence Day parade in the town, the agency said, but the blast was not dangerously close to the parade ground.
Police are treating militant separatists of the United Liberation Front of Asom (ULFA) as the main suspects in the attacks. The movement earlier called for a boycott of India's celebrations of liberation from British colonial rule, and threatened terrorist attacks. Local police have launched a large-scale security operation.
In the past three days 36 people have been killed in militant attacks in the province, of which 28 were Hindi-speaking workers from other states, the news service said.