27 EU leaders meeting in Brussels had agreed to let internal preparations for the second phase of Brexit talks with London, dealing with trade, Donald Tusk said.
Austria's Sebastian Kurz assured EU leaders on Thursday of his support for the EU, allaying concerns that his country would become a dissonant voice in the bloc.
PM Theresa May said she would tell fellow EU leaders on Thursday of "ambitious plans" for progress in Brexit negotiations in the coming weeks.
EU leaders will on Thursday reaffirm their full commitment to the 2015 nuclear deal between Iran and world powers, regardless of US criticism.
Theresa May to fellow EU leaders in Brussels on Thursday as she tries to break a deadlock in Brexit talks.