A rebel group calling itself the "New IRA" knows a bomb attack would hijack global headlines, The Sun reported.
British Prime Minister David Cameron, US President Barack Obama and Russian President Vladimir Putin will be among those meeting in Enniskillen in June.
German Chancellor Angela Merkel, French President Francois Hollande, Canadian Prime Minister Stephen Harper and Japanese Prime Minister Shinzo Abe will also attend.
Italian Prime Minister Mario Monti, if re-elected next month, is also expected there.
The terror group plotting to wreck the summit has 700 members, security chiefs said.
Five militant groups have joined forces to form the New IRA.
The summit will be held at the five-star Loch-side Lough Erne hotel in Enniskillen.
"We are very confident that the G8 venue is completely secure. But we can't rule out the possibility of some kind of cowardly attack in another part of the province," a British official said.
An attack on the British mainland remains on the agenda of the group but it currently lacks the organisational capability, the daily said.
The group is reportedly making bombs that can pierce armour plating before exploding.
Three such devices - designed to kill people inside armoured vehicles - have been seized this year.
London: Assassins from the dreaded Irish Republican Army (IRA) are plotting a terror attack as world leaders gather for a G8 summit in Northern Ireland, a media report said Wednesday.
First Published: Wednesday, January 30, 2013, 18:57