Eleven persons, including five paramilitary personnel, were also injured in the two incidents, which took place within the radius of about 100 kms.
In the first incident, the ultras attacked a polling party near Ketulnar village at about 11 am when it was returning after voting in the region, Additional Director General of Police (Naxal Operation) RK Vij said.
Polling was held in the Naxal-affected Bastar constituency on April 10.
When the election team reached near a pond in Ketulnar village between Gudma and Kutru, the Naxals triggered a landmine blast, he said.
"Six polling personnel were killed on the spot while another succumbed to injuries at a local hospital," the ADG added.
The ADG further added that the five others injured have been admitted to a local hospital in Bijapur and the bodies were yet to be retrieved from the forest.
The rebels fled to the forest after security personnel launched a retaliatory attack. Reinforcements were rushed to the spot and efforts are being made to retrieve the victims from the jungle, he said.
A police official said that around 75-100 armed rebels were involved in the ambush on the polling party. The rebels fled to the forest after security personnel launched a retaliatory attack.
Reinforcements were rushed to the spot, the ADG said.
Within an hour of the attack, the rebels blew up an ambulance carrying CRPF personnel under Darbha police station.
The incident took place in Kamanar village when around nine CRPF personnel were travelling in 108 Sanjeevani ambulance, he said.
Five CRPF personnel and the ambulance driver were killed in the incident, the ADG said.
Besides, five paramilitary personnel and a paramedic staff of the ambulance were also injured in the incident, he added.
According to a senior police official, the personnel belonged to 80th battalion of Central Reserve Police Force and were heading towards Jagdalpur district headquarter after a security operation in the region.
Meanwhile, some of them took lift in the ambulance ahead of Kamnar. The ultras were apparently keeping an eye on the movement of security forces following which they targeted the vehicle, he said.
The slain CRPF personnel have been identified as Inspector M K Rai, Assistant Sub-Inspector Kanti Bhai, Head Constable's Sitaram and M Umesh, Constable Dinesh and the civilian driver Vasu Sethiya.
After triggering a landmine blast, the Naxals opened indiscriminate firing on the bus.