British Prime Minister Theresa May should clear up what financial commitments Britain is willing to honour as part of its divorce agreement with the European Union, Dutch Prime Minister Mark Rutte said on Thursday.

"Theresa May has to come up with more clarity on what she means by 'other commitments' in her Florence speech. I phoned her last week, and tried to encourage her to do that and so far she hasn't," Rutte told reporters on arriving at an EU summit.

Asked if the clarification was needed on money, Rutte said:

"Yes, primarily, and about citizens rights and border controls -- these are still difficult issues, but particularly the question of the exit bill," he said.