According to sources, many residents of the town fled to Cameroon as a result of the attack.
Rann shares a border with Cameroon.
Heavily armed fighters were said to have stormed the town in the early hours of Monday.
Details of the attack are still sketchy but they reportedly set many houses on fire and engaged troops in a fierce gun battle.
A resident said the insurgents allowed civilians to leave the town unharmed.
Another source said the ISWAP fighters fled the town following a military reinforcement.