US President Barack Obama did his bit to bridge sectarian divides Monday in a painting class with primary schoolchildren, pushing reconciliation in Northern Ireland.

British Prime Minister David Cameron, who is hosting the G8 summit, took Obama to a school in Enniskillen, a town once the site of one of the most notorious bombings in the long, dark decades of republican-unionist violence known as the "Troubles".

The two world leaders joined a group of kids working on a large painting, and both started wielding brushes with their left hands.

"I didn't realise that David was going to move so fast," Obama quipped, looking across at Cameron who quickly finished his part of the painting.

"I think I just went outside the lines," Obama said.

Going across lines, of a sectarian nature, was a key theme of Obama's short visit to Northern Ireland, in a speech in which he urged the young people of the province to heal divisions to safeguard the fragile peace.

"If towns remain divided -- if Catholics have their schools and buildings, and Protestants have theirs -- if we can't see ourselves in one another, if fear or resentment are allowed to harden, that encourages division," he said.

"It discourages cooperation," Obama said earlier, in a speech at Belfast's Waterfront Hall.

The Enniskillen school, which opened in September 1989, is what is known in Northern Ireland as an "Integrated Primary School". Its 245 pupils are balanced between Protestants, Catholics and other faiths.

Only six percent of schools in Northern Ireland are integrated -- the vast majority of pupils attend schools which are either Catholic or Protestant-run -- in a scenario that critics say perpetuates sectarian divides despite an end to most of the violence.

Enniskillen was the scene in November 1987 of one of the most horrific attacks of the Troubles, when an Irish Republican Army bomb exploded near a war memorial to British soldiers, killing 11 people and injuring 63 others.

Obama and Cameron, ahead of the tough business of the G8 summit at the nearby Lough Erne resort, focusing on Syria and the world economy, also asked the children what they knew about the meeting.

Several pupils, aged between nine and 11 years old, said leaders were talking about global poverty, hunger and issues like terrorism.