BELFAST (Reuters) - The European Union has long aided efforts to heal the deep divisions that plague Northern Ireland, and many people on both sides of the sectarian rift fear what might happen when Brexit forces it to walk away.  Since a 1998 peace deal ended three decades of violence between Protestant pro-British unionists and Catholic Irish nationalists, in which 3,600 died, the EU has pumped about 1.5 billion euros ($1.8 billion) into projects to shore up that peace - more than any other body apart from the British state. It has enjoyed broad support and influence as a force viewed by both sides as a neutral broker separate from the British government, which is distrusted by many nationalists, and the Irish government, distrusted by many unionists. It has been able to take on projects others shy away from, such as the reintegration of former militants, both IRA and pro-union loyalists, and support for relatives of dead fighters.      Brexit is already rattling the region by raising concerns it will lead to a hard border with EU member Ireland. For some in both communities, the idea of a new, rigid frontier stirs painful memories of the British Army watchtowers and checkpoints that peppered the border during the decades of bloodshed.  It s a very fragile situation here, and in Westminster there seems to be a lack of consideration for Northern Ireland,  said Kate Clifford, director of the Rural Community Network, a community group that has received peace funding in the past.  Without a (EU) peace program behind that, without the impetus of the external force that is Europe, that honest broker, things will become very difficult,  she said.   While no one expects a return to the widespread violence of Northern Ireland s  Troubles  of the 1960s to 1990s, sectarian tensions still run high and intermittingly erupt into rioting.   Some British ministers argue that savings from leaving the bloc would allow the government to match all EU funding and last month British Prime Minister Theresa May said that her government would consider replacing that European money.  Yet London has offered no guarantees and, with Brexit negotiations between London and Brussels in their infancy, there is little certainty about how leaving the bloc will affect Britain s finances.   The British government s Northern Ireland office and the EU s Belfast office declined to comment. Since the EU s Northern Ireland PEACE program was founded in 1995, funded groups have worked with hundreds of thousands of Northern Ireland s 1.8 million citizens on conflict resolution, anti-sectarianism and supporting victims.  By the end of its latest funding drive, it will have pumped in 1.5 billion euros. This makes it by far the largest funder of organizations working on peace projects outside the British government, which has provided several billion euros worth of funds to the sector but does not provide a single figure for its investment.  For many such groups, the EU represents their largest single source of funds.  The EU has separately funded major infrastructure projects to the tune of billions of euros, including the 250-metre pedestrian bridge that links the mainly Protestant and Catholic sides of the River Foyle at Londonderry, the city where many see  The Troubles  of having first exploded in 1969.  While critics have at times questioned whether the bloc has spread its resources too thinly, its role is widely acknowledged as transformative for the region, particularly funding groups that have worked with thousands of former fighters and relatives of militants who died in the conflict.    A lot of energy was put in to supporting the process whereby these groups which were previously killing each other were working together,  said Avila Kilmurray, who managed EU PEACE funding for the reintegration of prisoners from the conflict from 1994-2014, as director of the Community Foundation for Northern Ireland.   The danger is that if there is that hiatus in terms of funding that makes it (the cooperation) much more difficult to actually maintain.   Many community workers voiced scepticism that Northern Ireland, already one of the British regions receiving the highest level of taxpayers  money, will remain a priority for the British government in the upheaval of Brexit.   In this work, I have met no one who actually believes that the Tory government care enough  to match the funding, said Kieran McEvoy, a professor at Queen s University Belfast s Institute of Conflict Transformation. At Belfast s most notorious flashpoint area - the streets between the fiercely loyalist Shankill Road and the nationalist Falls Road - former militants from both sides now work together.  Some bring children from both communities on joint holidays and contact each other during street trouble to try to calm the situation when matters start to get out of control. EU funding has been  absolutely critical  for projects that involve ex-militants, said Seanna Breathnach, a former IRA member. He works for the Coiste, which helps former fighters reintegrate into society and get jobs after leaving prison.   Activists say former prisoners have been able to influence the kind of young men who might be tempted to join dissident militants opposed to the peace deal.   The key is that young people are not sucked in - that we stop the glamorizing of violence that some people do,  Breathnach said.  Post-Brexit, activists say they will be faced with two main problems: convincing the British political establishment that Northern Ireland still needs a disproportionate level of state spending two decades after the peace; and to ensure Northern Irish politicians don t shy away from difficult projects. Kenny Donaldson is director of the South East Fermanagh Foundation, a support group for victims of militancy which gets 40-50 percent of its funding from the EU.  His fear, he said, was that many in the British political establishment did not appreciate how fragile Northern Ireland remained, with communities still harboring deep distrust of each other  We have to make that step from coexistence in isolation to meaningful integration,  he said.  While you only have coexistence you are too close to violence.   