Dominic Raab has surprised EU officials and diplomats by optimistically claiming the Brexit talks are “closing in” on a solution to the Irish border problem, following a 30-minute telephone conversation with Michel Barnier.

In an an article on Thursday, in which he had threatened to withhold the UK’s £39bn divorce bill, the British cabinet minister had told how he was looking forward to continuing negotiations with Barnier the following day.

In reality, the two men had a call that lasted about 30 minutes on Friday, sources said. EU diplomats in Brussels also expressed astonishment at the sunny outlook offered by the British cabinet minister over the state of the negotiations.

In a statement issued after the call, Raab said: “This morning, I had an extended phone call with Michel Barnier. We discussed the latest progress our teams have made on the withdrawal agreement and the framework for the future relationship.

“While there remain some substantive differences we need to resolve, it is clear our teams are closing in on workable solutions to the outstanding issues in the withdrawal agreement, and are having productive discussions in the right spirit on the future relationship.”

EU diplomats suggested that in reality there was a complete impasse on the most difficult issue of finding a backstop solution that will ensure a lack of hard border on the island of Ireland, whatever the outcome of the future trade negotiations.

In a tweet that hinted at the lack of movement, Barnier said:

Michel Barnier (@MichelBarnier) Useful dialogue w/ @DominicRaab this morning on the progress our teams have made this week on the #Brexit WA. But substantive differences remain on the Protocol for IE/NI, governance and GIs. We are also continuing our discussions to find common ground on the future relationship.

The UK has rejected the EU’s proposal to in effect keep Northern Ireland in the customs union and single market after Brexit, but has not yet delivered on the prime minister’s promise to offer a workable alternative, Brussels claims.

In response to Raab’s comments, one senior diplomat said he hoped that the words were a sign that the UK was coming round to the proposal to simply “de-dramatise” the EU’s version of the backstop. “But that is not what Barnier is signalling to me,” the diplomat added.

Barnier wants both sides to illustrate to opponents of the EU backstop just how few checks in the Irish sea there would be due to the relative low level of trade between Northern Ireland and the rest of the UK.

A second EU diplomat told The Guardian: “In reality this is a matter of who blinks first. And we don’t think it is going to be the EU.”

The source added: “Nothing is going to happen until after Tory party conference on their end.”

A third said of Raab’s optimistic comments: “On the contrary my understanding is that the UK is refusing to discuss details of how the backstop could function. The EU will continue insisting on that”.

Raab suggested in his statement that the highest talks would be put on hold for a week, while EU leaders meet in Salzburg for a summit.

Theresa May is due to present her thoughts on the state of the talks over dinner on Thursday night before the EU leaders discuss the outstanding issues over a two-hour lunch the following day.

“We agreed to review the state of play in the negotiations following the informal meeting of heads of state or government of the European Union in Salzburg next Thursday”, Raab said, “and we reiterated our willingness to devote the necessary time and energy to bring these negotiations to a successful conclusion.”

Both Barnier, and most recently the European commission president, Jean Claude Juncker, have also dismissed the central planks of the prime minister’s Chequers proposals of a common rule book on goods and a customs arrangement that would allow the UK to enjoy frictionless imports and export and an independent trade policy.