DUBLIN (Reuters) - Northern Irish protestant politicians who are propping up British Prime Minister Theresa May’s minority government reacted with fury on Friday to a report that Ireland wants the Irish Sea to be its effective border with Britain after Brexit.

FILE PHOTO: Anti-Brexit campaigners, Borders Against Brexit protest outside Irish Government buildings in Dublin, Ireland April 25, 2017. REUTERS/Clodagh Kilcoyne/File Photo

Irish Prime Minister Leo Varadkar on Friday confirmed his government would oppose any customs posts or immigration checks on the land border between the Republic of Ireland and Northern Ireland, but he did not say where they should be placed instead.

His foreign minister, Simon Coveney, said there was no sea border proposal. But he did not say where he wanted to locate the customs and immigration checks that will be inevitable if Britain leaves the European Union’s single market and customs union.

The issue of how the Republic and Northern Ireland will fare after Britain leaves the EU is particularly sensitive given the decades of violence in the province over whether it should be part of Britain or Ireland. Around 3,600 people were killed before the 1998 peace agreement.

The Times newspaper sparked the row with a report that the Irish government’s preferred option was for customs and immigration checks to be located away from the land border and at ports and airports, effectively drawing a new border in the Irish Sea.

Northern Ireland’s Democratic Unionist Party (DUP) - the Protestant party propping up British Prime Minister Theresa May’s minority government angrily rejected the idea.

“There is no way that the DUP would go for an option that creates a border between one part of the United Kingdom and the other. Dublin really needs to understand that the proposition is absurd, it’s unconstitutional,” DUP MP Jeffrey Donaldson told BBC Radio.

Ian Paisley Jr, one of the 10 DUP members of the British parliament allowing May’s government to stay in power said on twitter that the Irish government’s opposition to high-tech border posts was for “a very hard border” returning to Ireland.

Former Northern Ireland First Minister David Trimble said in an interview with Sky News that Ireland was risking doing “enormous damage” to relations between Dublin and Belfast, .

In a ratcheting up of Irish rhetoric around Brexit, Varadkar said it was the Ireland rather than unionists that should be angry at British plans to reimpose an “economic border” across the island of Ireland for the first time in 25 years.

“As far as this government is concerned there shouldn’t be an economic border. We don’t want one,” Varadkar told reporters at a briefing in Dublin.

Politicians in London, Dublin, Belfast and Brussels have all said they want to avoid the return of a “hard border” on the divided island, although no progress has yet been made.

The current border between the Irish Republic, a member of the European Union, and the British province of Northern Ireland would become the only land frontier between the U.K. and the EU once Britain left the bloc in early 2019.

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There have been no customs or immigration checks on the 500-kilometer border since the European single market came into effect in 1993 and about 30,000 people cross every day without any border checks.

The Irish government has pointed out that any hindrance to cross-border trade would hit Northern Ireland harder with the Republic accounting for 25 percent of Northern Irish exports outside the UK, compared with just 1.4 percent going the other direction.

Overall, 52 percent of voters in the United Kingdom voted in favor of leaving the EU in last year’s referendum, but 56 percent of those voting in Northern Ireland supported remaining in the bloc.

(Corrects Coveney to foreign minister, paragraph 3)