Theresa May is to travel to Brussels later for a dinner with EU leaders in a bid to end a stalemate over Brexit.
The meeting, with chief negotiator Michel Barnier and Commission chief Jean-Claude Juncker, comes days after the pair said talks were in "deadlock".
Brexit Secretary David Davis will join Mrs May for the meeting, ahead of this week's summit of EU leaders.
On Sunday, the PM phoned German chancellor Angela Merkel in a further attempt to break the impasse.
Downing Street said Mrs May and Mrs Merkel agreed on the "importance of continued constructive progress" in the UK's exit negotiations in the early morning phone call.
Although Mrs May's trip was not made public during last week's negotiations, Downing Street sources insisted it had "been in the diary for weeks".
Over dinner, the PM hopes to end a stalemate over the settlement that is stopping the post-Brexit trading relationship being discussed.
She hopes when EU leaders meet on Thursday and Friday, they will give Mr Barnier a mandate to start trade talks.
But Mr Barnier said he would not recommend that talks move on to the next stage when he attends the European Council on Thursday.
Speaking after the fifth round of trade talks in Brussels, he said there was no agreement on how much the UK should pay the EU when it leaves.
He said: "On this question we have reached a state of deadlock which is very disturbing for thousands of project promoters in Europe and it's disturbing also for taxpayers."
Mr Juncker added that the Brexit process would take "longer than we initially thought", blaming delays on the UK's failure to settle its financial obligations.