Britain formally triggered the Brexit process on Wednesday and has called for simultaneous talks on exit terms and future trade ties.
But, speaking in Malta on Friday, Tusk insisted that sufficient progress would have to be made on the terms of the UK exiting the UK before substantive talks on other issues begin.
He told a news conference, "There is no such thing as a Brexit bill but I want to be clear that it will be the 27 remaining member states who will decide if sufficient progress has been achieved in the negotiations."
The former Polish Prime Minister outlined the EU's draft negotiating guidelines on Brexit.
He pointed out these would apply to an EU 27 "because from Wednesday, after triggering article 50, the UK is now on the other side of the negotiating table."
Tusk added, "We have worked very fast, because the treaty gives us only two years to reach an agreement."
He said the EU's principles, or red lines, should be treated as fundamental and the EU would "firmly stand by them."
The guidelines argue for a phased approach in the upcoming talks with the UK.
He told reporters, “"Our duty is to minimise the uncertainty and disruption caused by the UK decision to withdraw from the EU for our citizens, businesses and member states. As I have already said, in essence it is about damage control.
"We need to think of people first. Citizens from all over the EU live, work and study in the UK. And as long as the UK remains a member, their rights are fully protected. But we need to settle their status and situations after the UK withdrawal with reciprocal, enforceable and non-discriminatory guarantees."
Tusk also said he wants to prevent a legal vacuum for European companies that stems from the fact that after Brexit the EU laws will no longer apply to the UK.
He added, "We will also need to make sure that the UK honours all financial commitments and liabilities it has taken as a member state. It is only fair towards all those people, communities, scientists, farmers and so on to whom we, all the 28, promised and owe this money. I can guarantee that the EU, on our part, will honour all our commitments. This is important for all sides."
Tusk also flagged up the issue of Northern Ireland and fears of a return to a hard border between the north and south of Ireland.
He said, "We will give special and serious consideration to this issue, not least as we are aware of the sensitivities involved on the Irish issue."
In the talks, he said the EU will seek "flexible and creative solutions" aiming at avoiding a hard border between Northern Ireland and Ireland.
He added, "It is of crucial importance to support the peace process in Northern Ireland."
Tusk said, "These four issues are all part of the first phase of our negotiations. Once, and only once we have achieved sufficient progress on the withdrawal, can we discuss the framework for our future relationship. Starting parallel talks on all issues at the same time, as suggested by some in the UK, will not happen."
On the future relationship he said the EU shared the UK's desire to establish a close partnership, adding, "Strong ties, reaching beyond the economy and including security cooperation, remain in our common interest."
He went on, "The talks which are about to start will be difficult, complex and sometimes even confrontational. There is no way around it. The EU27 does not and will not pursue a punitive approach. Brexit in itself is already punitive enough. After more than 40 years of being united, we owe it to each other to do everything we can to make this divorce as smooth as possible."
He said he and UK Prime Minister Theresa May had agreed to stay in close and regular contact throughout the process and that he would visit her in London before the April European Council in Brussels.
Speaking at the same press conference, Malta's Prime Minister Joseph Muscat stressed that Michel Barnier would be the main point of contact between the EU and UK during the talks.
He also underlined the importance the EU attaches to the UK meeting its commitments before it finally exits the EU. "This is acknowledged in the letter Mrs May sent to Mr Tusk this week and these commitments must be respected," he declared.
Muscat also agreed that sufficient progress on the separation agreement with the EU was needed before any trade talks could commence.