Abba, who gave the order in a statement signed by the Force Spokesman, Mr Emmanuel Ojukwu, on Wednesday, confirmed that one policeman died in the incident, while three others sustained injuries.
The I-G directed the AIG in charge of Zone 6, Calabar, Mr Johnson Ogunshakin, to take over the investigation and promptly bring to book all perpetrators, conspirators and sponsors involved.
He expressed deep regretted at the death of policemen in the course of providing safety for the electoral process and sympathised with the families of the slain officers.
Abba further directed that all suspects arrested in connection with violence across the country should be prosecuted.
He noted with grave concern that in spite of serious warnings, advice and interface with political actors to avoid acts of violence in the ongoing electoral process, such acts had continued.
He, however, restated the resolve and commitment of the force to provide level playing ground for all political parties in line with its constitutional and statutory mandate.
Okrika is the hometown of Patience Jonathan, wife of President Goodluck Jonathan.
The shooting incident at the APC rally on Tuesday was the third time the party would be attacked.
On 11 January, the APC’s office in the town was bombed.
Less than two weeks after, a podium erected for a scheduled APC rally was also bombed by yet to be identified hoodlums.