He also said that EU leaders at Wednesday's working dinner expressed determination to protect European companies from new USA sanctions on Iran. "We have a lot of candidates for membership, but Serbia and Montenegro are in the first place".
The EU-Western Balkans summit in Sofia on Thursday wasn't supposed to talk about the enlargement but should have given a clear stance for the countries of the Western Balkans that the European Union counts on them and that it sees their future in EU membership, Slovak Prime Minister Peter Pellegrini (Smer-SD) said after the end of the informal summit in Bulgaria, in the country now chairing the EU Council.
"Next year the United Kingdom is leaving the European Union, but we are not leaving Europe - and we will continue to work with our allies to protect our collective security and champion the European values that so many in Macedonia and the wider Western Balkans share".
Mrs May and Mr Zaev will also discuss the ongoing dispute with Greece over the country's name - a northern area of the country is also called Macedonia, and Greece has been calling for a name change since 1991. Officials from the two countries have been locked in talks over the issue.
Representatives from Greece and Macedonia met on the fringes of the Sofia summit in an attempt to finally come to an agreement.
She said: "There' no intention to intervene in any way".
But, highlighting how long and hard their road to membership is likely to be, Prime Minister Mariano Rajoy of European Union member Spain stayed away from the talks since Madrid refuses to recognise the independence of Kosovo.
The EU is also wary of admitting new members before they settle their differences, particularly in a region still bedevilled by the aftermath of the bloody break-up of Yugoslavia in the 1990s.
The three-page document itself contained words about the "shared commitment to European values", the "unequivocal support for the European perspective" of the Western Balkan states and the commitment to "the primacy of democracy and the rule of law".
Without revealing a potential date, German Chancellor Angela Merkel said they have a "clear" route in.
Leaders of the Western Balkan countries signed a statement supporting the digital agenda for their region.
Albania would have to cut out crime syndicates from operating out of their country if they are to stand a chance at securing European Union membership.
"What really matters is the determination of applicants in implementing reforms. And patience because also on the European Union side you need to have the right window of opportunity to take the decision".