Donald Tusk, the President of the European Council, leaves after meeting Britain's Prime Minister, Theresa May inside 10 Downing Street, in central London, Britain April 6, 2017. REUTERS/Hannah McKay

BRUSSELS (Reuters) - The European Union will only be able to conclude talks on Britain’s exit if it stays united, which means the bloc’s unity is in Britain’s interest, the chairman of EU summits Donald Tusk said on Saturday.

Speaking to reporters before an EU summit to approve EU guidelines for negotiations with Britain, Tusk repeated the 27 countries remaining in the EU wanted a “close and strong future relationship” with London.

“There is absolutely no question about it. But before discussing the future, we have to sort out our past. We will handle it fairly. It is the only possible way to move forward,” he said, referring to Britain’s financial commitments to the EU budget, made well before the decision to leave.

“We need to remain united as EU 27. It is only then that we will be able to conclude the negotiations, which means that our unity is also in the UK’s interest,” he said.

Tusk said the EU wanted solid guarantees for all citizens and their families who will be affected by Brexit in Britain and in the EU -- a total of around five million people.

“This must be the number one priority for the EU and the UK. The Commision has already prepared a precise and detailed list of citizens’ rights we want to protect,” he said.

Tusk said this position had strong support from all EU institutions and the 27 governments.

“I know this is something unique, but I am confident it is something that will not change,” he said.