In the letter seen by AFP, he said the EU had been too slow to deal with the migration crisis, adding, "We do not have too much time to spare. Bratislava will have to be a turning point in terms of protecting the Union's external borders."
The five-page invitation letter was sent to leaders on Tuesday, on the eve of the annual State of the Union address by European Commission head Jean-Claude Juncker to the European Parliament in Strasbourg.
Tusk said the EU leaders meeting in Bratislava, in a summit that is meant to draw up a roadmap for a future without Britain, had to act now to secure Europe's borders in the face of the migration crisis.
"All too often they (European citizens) heard politically correct statements that Europe cannot become a fortress, that it must remain open," the former Polish prime minister warned.
Tusk added that it was important for the rest of the EU to learn from Brexit, especially the British people's concerns over mass migration.
He said the Leave camp in Britain's June 23 referendum used false arguments but said it was also true that the Brexit vote is a desperate attempt to answer the questions that millions of Europeans ask themselves daily.
"Questions about the guarantees of security of the citizens and their territory, questions about the protection of their interests, cultural heritage and way of life," he said.
"These are questions we would have to face even if the UK had voted to remain," he added.
Tusk, fresh from a tour of European capitals to canvass opinion, urged the EU to deliver on both security and prosperity but said that did not mean more powers for Brussels.
"My talks with you clearly show ... That is not the desired recipe," Tusk wrote
His last comments could be taken as a dig at Juncker, who has made much play of the fact that he leads a political Commission, rather than the bureaucratic apparatus it is by tradition, and as a result has been harshly criticised for not doing enough to prevent Brexit.
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