The EU objects to what it sees as UK attempts to link the Northern Ireland issue to negotiations on future trade | Charles McQuillan/Getty Images EU to UK: Don’t use Northern Ireland as bargaining chip in Brexit talks The EU objects to what it sees as UK attempts to link Northern Ireland issue to negotiations on future trade.

The EU warned British negotiators arriving in Brussels next week for the third round of Brexit talks that they should not use the Northern Ireland peace process as a "bargaining chip" to try to speed up Brexit talks.

Both the EU and the U.K. have underlined their commitment to the peace process, but there are concerns in Brussels that London is attempting to tie the future state of the Good Friday Agreement to talks on what the U.K.'s future trading relationship with the EU will look like.

Referring to a position paper on the Northern Irish border published last week by the British government, a senior EU official, who briefed reporters in Brussels Friday, objected to London linking the issue to negotiations on future trade. "We are a bit concerned by the combination in the U.K. paper between the preservation of the peace process and the future of the EU-U.K. trade relationship," the official said. "It is very important that the peace process does not become a bargaining chip in these negotiations."

In Britain, a spokesman for the Department for Exiting the European Union said the U.K. position paper on Northern Ireland "puts protecting the Good Friday Agreement at the heart of our approach."

"That includes a proposal that the U.K. and EU should agree upfront on the crucial importance of avoiding a hard border for the peace process in Northern Ireland," said the DExEU spokesman.

A DExEU official added: "This type of language suggests they don't properly understand the sensitivities or appreciate the human costs behind the hard-won progress in Northern Ireland."

"This is not some sort of game with bargaining chips. The third round of negotiations begin next week and we enter those discussions ready to make progress."

The U.K. has been pushing for the Brexit talks to move on to the country's future relationship with the EU, including trade and customs arrangements. But the EU has said it will only do so once the negotiations on Britain’s financial obligations, the rights of EU citizens residing in the U.K. and how to manage the Irish border after the split have made "sufficient progress." A decision on whether they have done so will be made in October at a summit of EU leaders.

The official said the EU's negotiating team, headed by Michel Barnier, would like Britain to come forward with a concrete methodology for calculating its financial obligations to reassure all the remaining 27 EU members.

Barnier “would be comfortable recommending sufficient progress” has been made if there is “a methodology sufficiently detailed” to calculate the EU’s exit bill, the official said, including some sort of legal analysis.

"We are indeed not looking at a number now, but we need to have these guarantees that the commitments to which the U.K. is a member will be honored," the official said.

British negotiators have said they intend to present their views on the EU's position orally next week, and that discussions on the financial settlement will focus on the U.K.'s involvement in the European Investment Bank and EU development funding.

A second senior EU official, who also briefed reporters, said if Britain leaves issues surrounding the financial settlement to the end of the talks "you increase the risk of failure rather than manage it."

An official familiar with the U.K.'s position said of the EU's proposals on the Brexit bill: "We didn’t find it a convincing case. Hugely unconvincing. We will go through all relevant legal provisions. They need to understand where we’re coming from. We will not be producing any numbers."

The official said the U.K. did not intend to produce a methodology for the bill. "In an ideal world they want to salami-slice us, step by step by step. And on you go, up and up, and there is the bill. That is not going to happen and we are not going to play that game."

Next week's session will include citizens’ rights, judicial and police cooperation and the U.K.'s plans to leave the nuclear energy agreement Euratom.

While it is hoped talks will “clarify” positions between EU and U.K. sides, “it is a very big gap,” the first EU official said.

Responding to questions over whether bank holidays had interfered with the schedule of talks, the official said: “We have not yet encountered a situation when lack of time will prevent us from advancing [discussions]. So far, it has been a lack of substance.”

This article has been updated with a response from the U.K. government.

Annabelle Dickson contributed to this article.