The talks between the U.K. and Europe are taking up too much time and the British negotiating side needs to step up the pace, a top EU official told CNBC Saturday.

Speaking in an exclusive interview on the sidelines of the Ambrosetti Forum in Italy, Jeroen Dijsselbloem, who leads the group of finance ministers for the euro zone, complained that Brexit "isn't going well."

"It's costing too much time and it's costing too much time for the British government to step up their pace," he said.

Negotiating teams concluded the third round of Brexit negotiations last Thursday, but Michel Barnier, the EU's chief negotiator, iterated that there hadn't been enough progress to allow talks to move to the next phase. The original timeline for Brexit talks had suggested that after October both sides would be in a position to discuss their future trading relationship, but discussions are still stuck on separation issues.

"I think you have to realize in the process of the separation that there will be a future relation that you can't walk away from it," Dijsselbloem said. "But we need to get through this phase (separation issues), let's make this phase as quick as possible with as little damage as possible."

Negotiations are supposed to focus for now on the future rights of EU citizens, the Irish border and the settling of accounts. But reports suggest the U.K. keeps insisting on discussing a future relationship between the two sides before settling these key separation issues.