BRUSSELS (AP) — European Union leaders are gathering in Brussels set to move Brexit talks into a new phase as pressure mounts on Prime Minister Theresa May over her plans to take Britain out of the 28-nation bloc.

Heated debate is also likely as the leaders thrash out whether mandatory refugee quotas should remain a part of the EU's response to the arrival of thousands of migrants in Greece and Italy.

They are also due to officially endorse a new system of defense cooperation, bringing order to the way nations cooperate on security matters.

A draft of their summit statement, seen Thursday by The Associated Press, says that progress made in Brexit talks "is sufficient to move to the second phase" to discuss future relations and trade.