The gunmen, on Thursday, laid siege on Uromi town in Esan Northeast local government area of Edo.
Witnesses said the gunmen, who stormed the town in several vehicles, attacked the four banks with dynamite.
The unmasked gunmen killed five persons and two police officers during the attack.
The police spokesman in Edo Bello Kontongs confirmed the attack but said he had no further detail.
According to Mr Kontongs, one of the financial institutions attacked was a new generation bank.
He also confirmed the killing of the two cops and five civilians in the attack.