Official sources said the first explosion was reported from interior Thoubal district at a fair ground, near the district headquarters, at around 8 am.
Four persons, identified as Y Manao Singh (52), Sanabanta Das (22), Akoijam Ongbi Sanajaobi Devi (55) and Ningombam Manisam Devi (65) were injured and taken to a nearby district hospital.
Their condition was stated to be critical, the sources said.
Three powerful bombs later exploded in the capital complex in Imphal during Chief Minister Okram Ibobi Singh's speech at the 1st Manipur Rifles parade ground. The ground is about two km away from the site of the bomb explosions.
The Chief Minister was appealing to insurgents to give up arms and join the national mainstream by participating in the development process.
Sources said a powerful bomb, allegedly planted by the insurgents at the side of busy road at Sagolband in the capital complex, was apparently set off by using a remote-controlled device at around 9 am, damaging the wall of a nearby house.
They said the bomb might have been planted to attack security personnel who used the road often to go to CRPF headquarters at Langjing, about 6 KM west of here.
Ten minutes later, another powerful bomb exploded at a place on Minuthong bridge on Imphal river in the capital complex, sources said, adding the place is about KM from the 1st Manipur Rifles parade ground.
Official reports from Thoubal district said minutes after the bomb explosion at Mela ground, police and paramilitary forces, including Assam Rifles personnel, surrounded nearby suspected areas and rounded up several persons.
All the detained were later freed after proper verification, the reports said. Passers-by at isolated places were also checked to detect movement of ultras who sneaked into nearby interior areas after the explosion, reports said.