The heads of government, meeting without a British representative for the first time in 40 years, said in a statement that Britain would be treated as a "third country" with both "rights and obligations".
Continued access for to the huge EU single market of 500 million people "requires acceptance of all four freedoms, including freedom of movement," EU president Donald Tusk told a news conference.
German Chancellor Angela Merkel has also warned that London cannot not "cherry-pick" the terms of the exit negotiations.
There are also concerns that with euroscepticism growing in many member states, giving Britain overly favourable divorce terms will spark a domino effect of others leaving the EU.
More From This Section
Cameron, who yesterday attended probably his last EU summit in Brussels, is also under pressure to quickly initiate divorce proceedings by formally telling the EU Britain wants to leave.
EU leaders say that until this notification is made, no talks can begin - formally or informally - on resetting Britain's ties with the EU, a process meant to last two years.
In an effort to prevent further exits, the leaders agreed today they need to do more to battle "dissatisfaction with the current state of affairs", their joint statement said.
"Europeans expect us to do better when it comes to providing security, jobs and growth, as well as hope for a better future," they said, announcing a "political reflection to give an impulse to further reforms".
"It might be in my party's interests for him to sit there, it's not in the national interests and I would say, for heaven's sake man, go," Cameron told Corbyn in a raucous parliamentary session.
Labour MPs voted against Corbyn in a no-confidence motion yesterday, with the veteran left-winger accused of not campaigning hard enough to convince the party's traditional working class voters to oppose Brexit.
Within the governing Conservatives, nominations opened today for a successor to Cameron. The race is expected to be a two-way contest between ex-London mayor and anti-EU campaigner Boris Johnson and interior minister Theresa May, who wanted to stay in the bloc.