The Irish border challenge in Brexit negotiations has to be solved by Britain, not the EU, the Swedish government has said.

The Swedish minister for EU affairs and trade, Ann Linde, said it was regrettable the Conservative party had made such an “extreme ideological” issue of the need to maintain the existing invisible border between Northern Ireland and Ireland after Brexit.

“I feel sorry that this issue of the backstop is being so extreme ideologically and difficult here. I think it is unfortunate that this backstop has become so loaded and a matter of ideology,” she told the Guardian.

She made her remarks just hours after a private meeting with the Brexit secretary, Dominic Raab, in London. “After our meeting [with Raab] it’s clear this issue is very, very difficult [for the Tories],” she said.

Linde said it was up to Britain to come up with a solution.

“As it looks now, we try to find what if there is any way for a soft border. I think this is for Britain to find out. Britain is leaving and it wants to make use of the single market, that’s in the white paper.

“The British have been talking about the technical solutions but little detail on the backstop,” she said.

Linde, who visited Dublin and Belfast in May to find out more about the border issue, said the impasse was “complicated to solve” but added: “It is not for us to figure out.”

She was speaking as it emerged that Jacob Rees-Mogg, the head of the hard-Brexit European Research Group of Tory MPs, said it would be possible to “inspect” people crossing the border in similar vein to checks during the Troubles.

His comments were branded “ill-informed” by the Irish deputy prime minister, Simon Coveney.

Linde said Britain already accepted checks on the Irish Sea for animal health so the opposition to different regimes in Northern Ireland and Britain post-Brexit was inconsistent on a policy level.

“As I see it, there are already border checks because Ireland is an island for example with animals,” she said.

There has been speculation that the EU would budge on its sequencing to see if an overall deal on customs and the single market would obviate the need for a backstop for Ireland.

However, Linde said the EU was insistent on a backstop, because it would operate as an insurance policy for Ireland whoever was in power in Westminster.

One idea floating in Dublin last week was for checks on goods going into Northern Ireland at British ports such as Liverpool and Stranraer. This would mean everything going on to the island of Ireland was already checked for compliance with EU rules and if the freight went on to the Irish Republic there would be no need for border checks, thus preserving the integrity of the single market.

However, this is unlikely to be acceptable to Brexiters,who are opposed to Britain conducting work on behalf of the EU on British soil.

Linde was in London to meet Swedish citizens over continuing concerns over their rights to remain in the UK post Brexit.

She said Raab had given her clear assurances that EU citizens could be allowed to stay in the UK but questioned whether they would retain the same rights.

“And I believe him. I really believe him,” she added. “But I do not know and he did not say if we have no withdrawal agreement, what rights people will have, like pension, sickness insurance etc,” she said.

After her meeting at the Swedish church in London she said Swedish nationals “felt a little bit assured by that”.

She also said the EU would not be dropping its insistence that there had to be a decision on Ireland before an overall withdrawal agreement.

“I have been to all the European affairs council meetings and the question of Ireland is there every time and every time people are united about this. We are very unified,” she said.

It will be raised again when the EU 27 meet in Salzburg on 18 September, she added.

The border issue has become a greater challenge since July this year when an amendment by Labour Brexit supporter Kate Hoey to the trade bill was nodded through by Theresa May.

Although it got little publicity amid the chaos of the knife-edge vote in July, it commits May to an autumn law making a border in the Irish Sea illegal, thus killing off the EU’s backstop proposal for special customs arrangements for Northern Ireland.