BERLIN (Reuters) - The foreign ministers of Germany and France have drawn up a nine-page document entitled "A strong Europe in a world of uncertainties" in which they propose common European security and migration policies and strengthened economic convergence.

"To prevent the silent creeping erosion of our European project we have to be more focused on essentials and on meeting the concrete expectations of our citizens," Frank-Walter Steinmeier and Jean-Marc Ayrault said in the paper, a copy of which was seen by Reuters.

Britain leaving the European Union makes it even more important the bloc presents a united front against growing global challenges, EU foreign affairs head Federica Mogherini said on Sunday.

"The purpose, even existence, of our Union is being questioned. Yet, our citizens and the world need a strong European Union like never before," Mogherini said in a global strategy review EU leaders will discuss at a summit next week.

"In challenging times, a strong Union is one that thinks strategically, shares a vision and acts together," she said. "This is even more true after the British referendum."

EU leaders last year tasked Mogherini with drawing up a "Global Strategy on Foreign and Security Policy" in response to a host of security challenges, chief among them Europe's worst migrant crisis since World War II.

The report was meant to be a top agenda item at the EU summit on Tuesday and Wednesday in Brussels but Britain's vote to leave the bloc has thrown everything up in the air.

Britain would be a key element in any more ambitious EU security strategy given its status as a nuclear-armed and veto-wielding permanent member of UN Security Council.

Only France matches this standing while Germany, the most powerful EU member state, is very wary of any foreign military involvement.

Mogherini has consistently argued that the EU should play a global role in keeping with its status as one of the world's largest economies.

But some 22 out of the current 28 EU nations are also members of Nato and when it comes to security, they look first to the US-led alliance. Mogherini stresses the need for cooperation with Nato but also wants the EU to stand more on its own two feet.

"The Strategy nurtures the ambition of strategic autonomy for the European Union. This is necessary to promote the common interests of our citizens, as well as our principles and values," she said in a foreword to the report.