European Union leaders are gathering in Brussels for a two-day summit. They will discuss ways to resolve the political and economic chaos following the UK’s vote to leave the EU.

The participants include British Prime Minister David Cameron, European Commission President Jean-Claude Juncker, and European Council chief Donald Tusk.

Tusk said that the union would not be able to begin negotiations on the exit until the British government has formally declared its intention to leave. He also said that the EU will hold a meeting in the Slovak capital of Bratislava in September to assess the future of the EU without the UK.

Earlier, Juncker urged the UK to clarify its position on Brexit as soon as possible. German Chancellor Angela Merkel also echoed the remarks. But Prime Minister David Cameron, who announced his plan to resign, insisted Britain will not pull the trigger until his successor takes his place in September.