The U.N. secretary-general is urging European leaders to act swiftly to address the growing migrant crisis during their emergency summit Thursday, and he says he will discuss the issue in his audience with Pope Francis next week.

Ban Ki-moon's letter to European Council president Donald Tusk urges European Union leaders to consider the U.N. refugee chief's proposals for a stronger EU search and rescue operation and more legal migration channels.

"We all have a moral imperative to act swiftly," Ban says in the letter obtained by The Associated Press. He says the "ruthless smuggling" of desperate people will continue along Europe's southern borders will continue without political solutions to crises in the Middle East and Africa.

Ban told reporters he and Francis will discuss how to work together on it.