Dublin - Ireland's main opposition party has submitted a motion of no-confidence in the deputy prime minister over her handling of a police whistleblower controversy, warning that elections loomed if she did not step down.

Irish Prime Minister Leo Varadkar, leader of the Fine Gael party that heads the minority government, has ruled out the resignation of his deputy Frances Fitzgerald. But opposition Fianna Fail leader Micheal Martin said there would be an election if she did not step down.

Fianna Fail props up the minority government, and the prospect of a snap election before Christmas looms if it removes its support.

Fitzgerald "should step aside in our view and that would avoid a general election," Martin told RTE public radio.

The motion will be voted on next Tuesday, pushing Varadkar's minority government to the brink of collapse ahead of a key summit next month with EU leaders where the issue of Ireland's post-Brexit border with Britain will be on the agenda.

Ireland is pushing EU leaders to ensure its concerns about the border with British-ruled Northern Ireland are taken into account before Brexit talks can continue, adding an unexpected hurdle to Britain's plans.

Irish foreign minister Simon Coveney arrived for a meeting in Brussels on Friday, accusing Fianna Fail of jeopardising the national interest.

"Fianna Fail are behaving recklessly here," he told reporters.

"We have a precarious situation with the main opposition party that signed up to a agreement in the country's interest... now effectively breaching that and risking an election at a time when there are some really, really serious issues for the government to manage," he added.

Arlene Foster, leader of Northern Ireland's Democratic Unionist Party, which props up the Conservative Party in Westminster, on Friday accused the Irish government of using the Brexit negotiations "to put forwards their views on" Irish unification.

"We have heard from the foreign ministry of the Republic or Ireland talking about his inspiration for a united Ireland," she told BBC Radio 4's Today programme.

"He should not be using the negotiations to talk about those issues."