EU Council President Donald Tusk said on Tuesday the April 29 summit would draw up guidelines in order to create "certainty and clarity" as both sides head into a period of extended negotiations.

A slight majority of Britons voted in a June 2016 referendum to leave the soon-to-be-27-member bloc. British Prime Minister Theresa May announced on Monday that she would trigger Article 50 on March 29, formally beginning the "Brexit" process, which is expected to take around two years.

EU leaders will then hold their summit - to which May is not invited - in order to get the most effective deal for both sides, Tusk said. "I personally wish the UK hadn't chosen to leave the EU but the majority of British voters decided otherwise," he said during a visit by Japanese Prime Minister Shinzo Abe in Brussels. "Therefore we must do everything we can to make the process of divorce the least painful for the EU."

On Twitter, he said the EU's priority would be to ensure "certainty and clarity" for all citizens, companies and member states.

Other EU leaders have made it clear that they want tough negotiations with May's government. "It cannot be like it was before, otherwise it would be a waste of time to have a Brexit. There will be consequences," said French Finance Minister Michel Sapin.

Tusk's comments came during a visit by Abe in Brussels

A 'historic event'

On Tuesday, May told her cabinet that her letter to Tusk formally triggering Article 50 would be a "historic event" and "one of the most important documents in our country's recent history."

A day earlier, a British government spokesman said the UK and the EU "are on the threshold of the most important negotiations for [the UK] for a generation."

Still, while the talks will be officially triggered at the end of March, the negotiations will not actually start until several weeks after the EU summit, when leaders from the bloc gives their Brexit negotiator, Michel Barnier, their mandate.

A European Commission (EC) spokesman said Barnier will update members of the EC with the state of preparations for Brexit talks on Wednesday.

blc/kms (AP, AFP)