EU leaders are set to gather on Thursday in Brussels for a spring summit that will focus on economy, security and migration.

Donald Tusk, the current president of the European Council, is widely expected to be re-elected, despite lacking support from his native Poland.

EU leaders will then take stock of: the European economy; the current situation in the Western Balkans; as well as defense and military cooperation.

Thursday's summit will probably be the last time European leaders gather before British Prime Minister Theresa May formally invokes Article 50, the mechanism for leaving the European Union.

After speculation that May would take a formal letter to the summit, she now looks likely to arrive empty-handed, as legislative maneuvering in London has delayed her timetable.

Britain wants to officially declare its intention to leave the EU by the end of March, triggering a maximum two-year period of negotiations.